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Reflectance Spectroscopy - Science method

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I study on some kind of infrared barrier and I don't know how to calculate normalized reflectance spectra weighted by human body radiation?
For example you can see results of this article but authors did not mention the calculation method:
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Respected all,
I have come across a few machine learning algorithms, for prediction of soil chemical properties such as pH, EC, Available nutrients. But, rarely the use of diffuse reflectance spectroscopy assisted by machine learning algorithms. can anyone suggest me some papers regarding the application of different ML techniques in Pre-processing and prediction of pedological properties in hyperspectral imagery.
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Is it correct to have reflection percentage higher than 100% or is the data not correct?
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Thank you so much.
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Hello,
I am currently designing an optical setup to perform measurements of reflected light (BRDF actually) and I am asking myself if I should consider a "focused on-sample" light beam or a collimated one. What are the influence of collimated and/or focused light on the signal after reflection ?
PS : I am considering diffuse reflection.
Thank you very much
Kind regards,
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You definitely want collimated light. A focused beam with its range of input angles hides features of the BRDF. For example suppose you have a mirror. A collimated input goes to a collimated output. These are essentially delta functions in angle space. However, if you put in a focused cone of light, you always at least get out that cone of light, a large range of angles in angle space regardless of the surface. Now say the mirror is slightly scattering. A collimated beam goes to a small diffuse cone. However the cone of focused light goes to a slightly fuzzier cone. The details of the BRDF of the surface are hidden in the large cone of the focused beam. In short, the angle measurement will be the convolution of the BRDF of the surface and the angular profile of the incident beam. If you want to measure the BRDF you want to convolve with as close to a delta function as possible.
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 either low or high band gap will give good NLO properties?
I have synthesised boron compounds and I investigated the band gap values using diffuse reflectance spectroscopy further I want to go for SHG NLO application. Thus how to help the band gap values for NLO application....... 
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larger the band gap, good will be the NLO activity
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Dear more experienced colleagues,
I do external reflection FTIR measurement of waxes on a polyethylene substrate (ski waxes on UHMWPE ski base). I'm wondering why peaks associated with for example C-F stretching peaks in case of fluorinated wax, or Si-O-Si and Si-C peaks in case of silicone-based wax do not have the derivative-like shape (as clearly seen for C-H peaks in the spectra), which is associated with the surface reflection. The shape has rather transmission/absorbtion-like shape, but is pointing up towards higher reflectance and not down, as would be the case if the IR light would be reflected from the PE substrate (which is not expected due to the similar refractive indexes of the waxes and the PE substrate). What is the physical explanation of such behaviour?
Thank you for any help!
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Hi Daniel,
the shape of the peaks in a specular reflectance spectrum depends on the oscillator strength. For peaks with comparably weak strengths, like those in organic and biologic matter, the absorption index function is also comparably weak, therefore reflection is dominantly influenced by the real refractive index function and the peaks have a derivative-like shape. For inorganic materials the oscillator strengths can be much higher and the same is true for the absorption index function, which increasingly influences the reflection spectrum until it dominates. Therefore the bands of oscillators with high strength are absorption index-like. If you want to learn more, check out my lecture notes:
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Two years ago, during my PhD defense one of the members of the committee asked me what diffuse reflectance is. I said diffuse reflectance is a type of surface reflectance (the other is specular reflectance) whose angle of reflection is independent on the angle of incident radiation. Diffuse reflectance is often observed with radiation incident on a mat or dull surface such as paper, tissues whereas specular reflectance is observed with radiation incident on a polished surface such as a mirror. This is a perfect text book definition
(ref Optical thermal response of laser irradiated tissue, A J Welch or Modern techniques in applied molecular spectroscopy by F. Mirabella)
However, my answer did not sit well with the committee, especially the “surface” part. They argued if diffuse reflectance is a surface reflectance than why diffuse reflectance spectroscopy (DRS) is used to detect tissue abnormality 300-400 micron underneath the surface? They came to agree that diffuse reflectance is “radiation that undergoes scattering and absorption events in tissue and comes back to the surface to be detected by detector”
I disagreed.
Just a few days ago, the same question is asked: what is diffuse reflectance? My answer is the same. Once again, there was lots of confusion.
Today, to put my mind to rest I am posting my explanation here. Again, diffuse reflectance is a type of surface reflectance (nobody can change that definition). The name diffuse reflectance spectroscopy (DRS) itself is quite confusing.
DRS collects not only the diffuse reflectance but also the remission. In clinical application of DRS, remission is frankly much more important because it tells us how light propagates within the tissue, and thus help us draw a picture of tissue components (scatterer, absorber). By the textbook, remission is the process in which light is scattered within the tissue, leaving tissue and propagating toward the detector. Therefore, remission is the result of complicated light propagation within the tissue.
This is, partially, why fiber optics DRS with fiber tip in contact with tissue plays an important role. The math is complicated. Principally, contact point of measurement DRS reduces chances to collect surface reflectance and increases chance to collect remission. DRS gave out-standing spectral resolution but not so much spatial information. So, there comes bundle of fibers in an optical probe that likely give enough spatial information to detect tumor margin.
Two tissue samples with different optical properties but same surface structure will have similar diffuse reflectance but different remission. As the results, different DRS signal is collected.
Next topic: Raw fluorescence signal that was not corrected for tissue attenuation is useless.
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Thank you for good discussion, is there any paper pointing out these information you mentioned V. N. Du Le ?
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I need information concerning the penetration and reflection capacity of ultraviolet and infrared radiation wavelengths on different most common materials.
Edit.
Can somebody recommend a book to learn about? I'm especially interested in spectrogroscopy with a city environment materials and albedo.
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First of all it depends to the material studied, and for me i guess that IR is more better then UV cause its wavelength is bigger than UV.
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Where is DRS diffusion reflectance spectroscopy available in India for the find the optical band gap of ferrite powder sample.
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By-election
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USGS provide two kind of major Data sets, which are collection 01- Level 01 and Level-02 data. In Level-02 data All the other visual bands are process to surface reflectance but why panchromatic band isn't process? My question is how to process panchromatic band to surface reflectance? Can you suggest the method for me?
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Hi Dulan,
Pansharpening is a process of merging high-resolution panchromatic and lower resolution multispectral imagery to create a single high-resolution color image. Google Maps and nearly every map creating company use this technique to increase image quality. Pansharpening produces a high-resolution color image from three, four or more low-resolution multispectral satellite bands plus a corresponding high-resolution panchromatic band:
Low-res color bands + High-res grayscale band = Hi-res color image
Such band combinations are commonly bundled in satellite data sets, for example Landsat 7, which includes six 30 m resolution multispectral bands, a 60 m thermal infrared band plus a 15 m resolution panchromatic band. SPOT, GeoEye and DigitalGlobe commercial data packages also commonly include both lower-resolution multispectral bands and a single panchromatic band. One of the principal reasons for configuring satellite sensors this way is to keep satellite weight, cost, bandwidth and complexity down. Pan sharpening uses spatial information in the high-resolution grayscale band and color information in the multispectral bands to create a high-resolution color image, essentially increasing the resolution of the color information in the data set to match that of the panchromatic band.
One common class of algorithms for pansharpening is called “component substitution, which usually involves the following steps:
  • Up-sampling: the color bands are up-sampled to the same resolution as the panchromatic band;
  • Alignment: the up-sampled color bands and the panchromatic band are aligned to reduce artifacts due to mis-registration (generally, when the data comes from the same sensor, this step is usually not necessary);
  • Forward transform: the up-sampled color bands are transformed to an alternate color space (where intensity is orthogonal to the color information);
  • Intensity matching: the intensity of the color bands is matched to the pan band intensity in the transformed space;
  • Component substitution: the pan band is then directly substituted for the transformed intensity component;
  • Reverse transform: the reverse transformation is performed using the substituted intensity component to transform back to the original color space.
Common color-space transformation used for pan sharpening are HSI (hue-saturation-intensity), and YCbCr. The same steps can also be performed using wavelet decomposition or PCA and replacing the first component with the pan band.
Pan-sharpening techniques can result in spectral distortions when pan sharpening satellite images as a result of the nature of the panchromatic band. The Landsat panchromatic band for example is not sensitive to blue light. As a result, the spectral characteristics of the raw pansharpened color image may not exactly match those of the corresponding low-resolution RGB image, resulting in altered color tones. This has resulted in the development of many algorithms that attempt to reduce this spectral distortion and to produce 'true color' imagery.
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In visible reflectance spectroscopy performed on a bovine tendon, peaks were observed corresponding to tendon amides. But I do not know these peaks are related to what kind of amides.
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Oh sorry Sir
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Reflectance can be used for remote-sensing of the presence of algae in water bodies. But is there any advantage in using reflectance over absorbance in the laboratory settings? I am interested in measuring algal pigment composition and content.What additional or superior information can I get from reflectance compared to absorbance?
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For the sake of comparisons and the available standardised procedures, it is preferable to use absorbance under laboratory conditions. Except if you have customised equations for spectroscopic reflectance at difference wavelengths, then you can make comparisons between reflectance and absorbance.The traditional absorbance methods are robust enough to give you an idea of the amount of pigment in your samples. If you are doing method development, then, it will be interesting to see your findings.
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I need it for the calculation of the colorspectrum dipendent of the oxide thickness
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Hi Armin,
I'm looking for the same properties of Ti-6Al-4V. Would you please let me know if you could find them?
Regards,
Eskandar
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I measured the transmissivity, absorptivity, and reflectance
parameters of samples using a Jasco V-670 UV-VIS-NIR Spectrophotometer. However, the reflectance values seemed unusual and incorrect.
The reflectance of a crystalline silicon (c-Si) 500 μm thick 2" wafer was measured for the region 0.25 μm to 1.8 μm. However, reflectance was reported as > 100% between 1.2 μm to 1.8 μm and 0.25 μm to 0.36 μm, with the overall mean reflectance for the measured spectra is 127%. See figure attached.
As I understand it, there are a few possibilities for what could be happening here: (a) a poor baseline that contains significant absorbances in the regions in question; (b) emission from the sample; (c) the device itself might need a different accessory to measure specular reflectance; or (d) high levels of specular reflection.
Of the four possibilities, I believe (d) is the most likely. The background reference used will have had very little specular reflection, but as the c-Si sample is a smooth, polished surface it might be quite high. A description of the issues this specular reflectance can cause is described by Blitz [1]. He also discusses the fact that Kubelka-Munk theory ignores specular reflectance completely, which may produce anomalous results.
Has anyone encountered this issue before? And if so, what did you do to solve, mitigate, or overcome the issue? Furthermore, are there perhaps any better alternatives to measure the reflectivity of a smooth, polished sample?
Any help or advice would be appreciated! Thanks in advance.
[1] J. P. Blitz, “Diffuse Reflectance Spectroscopy,” in Modern Techniques in Applied Molecular Spectroscopy: Techniques in Analytical Chemistry (F. M. Mirabella, ed.), ch. 5, pp. 185–219, New York: John Wiley & Sons, 1998.
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Thanks a lot.
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HOPG is a good substrate for growth of h-BN. One major application of h-BN is single photon emission which can be used for telecom wavelength. Can anyone give me any insight about the absorption quality(if there is any) of HOPG at 1550 nm.
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HOPG is an unpolar substance, so it is not exactly great at absorbing infrared radiation which is why people usually characterize it by Raman spectroscopy. Here you can find extrapolated dielectric functions:
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For polymer film samples, if reflectivity and transmissivity in the mid-infrared region (here, 4 to 16 micrometers) are desired, and using a FTIR & ATR spectrometer (Bomem MB Serie Hartmann & Braun) :
1-Is it possible to use the output spectrum to evaluate the reflectivity and transmissivity?
2-Should not the baseline be corrected by OMNIC Software? Using normalize scale is not allowed?
3-If there are more than 100% reflection in some cases, what corrections should be made? Thanks*
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Even better, there are programs available with which you can analyze your spectra. E.g RefFIT by Alexey Kuzmenko (https://reffit.ch/) or CODE by Wolfgang Theiss (https://www.wtheiss.com/). Both have good manuals. Also SpIRIT by Konstantin Shportko (http://www.shportko.com/spirit.html) should be up to the task.
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I am trying to calculate the optical band gap, valance and conduction band energy levels of my sample. I found that optical band gap can be calculated using kubelka-munk function and diffuse- reflectance spectroscopy. Also, I find that the valane band energy levels can be driven from valance band XPS method, but i was not able to find more details. So, this is my question:
for calculation of valance band energy using XPS analysis, i need to conduct specific kind of XPS analysis? how i can apply XPS plot to use valance band energy?
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First of all, let me remark that UPS is a much better method for the investigation of valence band energies since the valence band has very low XPS cross sections and therefore you will end up with way too large error bars on your results.
If you have only XPS available, you proceed as follows:
Let us assume you have the usual setup: grounded sample, constant excitation energy, kinetic energy is measured with a CAE analyzer. Since you seem to be investigating a semiconductor I assume you are not troubled by charging effects.
Then your binding energy with respect to the Fermi energy is
EB=Erad-Ekin
In order to proceed, the ionization potential corresponds to the sum of the work function of your material and the binding energy of the first peak edge in your spectrum.
For more details, you can either refer to standard textbooks such as Ertl/Küppers or Hüfner (but the latter one is probably too deep for a starter) or check out manuals of analyzers. The Omicron manual is very good:
and for more details (especially baselines and peak fitting) the Casa XPS manual is actually more concise and helpful than any textbook I know:
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When imaging protein solutions (1ug/ml,10ug/ml,100ug/ml,1000ug/ml ; diluted with PBS buffer 7.4) on a gold surface, what is the optimal pretreatment(s) to separate out the effect of the buffer (in my case PBS) which interferes with bands of interest for proteins?
10ul of each concentration was dropped on a clean gold slide and allowed to dry for 24hr under Nitrogen purge, followed by FTIR-reflectance imaging.
Since samples with 1000ug/ml are highly concentrated, their signal appears very clear (Amide I, Amide II, Amide III, Amide A, Amide B), however at concentrations below and = 100ug/ml, protein signature is dominated by PBS buffer bands.
What kind of univariate or multivariate methods would you apply to
(a) identify protein pixels (remove interference of buffer, slide background if any)
(b) quantify protein pixels (eg. make PLSR model on 0ug,1ug,10ug,100ug,1000ug) and predict concentration level of an unknown dried protein sample?
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After drying you most probably get a coffee ring effect, meaning that the thickness of you layers is strongly changing from point to point. Therefore imaging and measuring individual points might in any way not be the correct method for reasons explained in
The electric field standing wave effect can be corrected as explained in
My feeling is, however, that you should better use a different technique, maybe to coat an ATR crystal and see if you could obtain a calibration line, in particular also, because for near normal incidence and thin layers, you might see nothing at all on your metallic substrate due to the fact that a metallic surface suppresses electric fields parallel to its surface. Certainly, this still does not solve the problem of overlapping bands.
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Dear experienced researcher,
I will briefly explain my experiment and then ask two questions I have.
The solution of particular interest is transition metal oxides (TMOs), especially Molybdenum Oxide MoO3. The way I prepare it by using solution synthesis method and thus the actual composition of molybdenum oxide is of the form HyMoOx. Theoretically speaking, the absorption of the HyMoOx should be varying with the change in the oxidation state of Mo, where MoO3 has lowest absorption while HyMoO2 will have more absorption due to reduced bandgap.
What I want to do is to use UV-VIS spectroscopy to characterize the form of the solution. Since, I have no experience in it, I want to go through some literature that uses the same technique to do this or something similar? I failed to find any useful papers about it, if there are, please share them to me?
Second, to characterize the absorption of the solution, a high transparent container should be used. Can any one share with me the high transparent glass container or other container are suitable for this experiment setup?
Regards,
Chenjin
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it seems unlikely that you mean solution. As mentioned above the metal oxides will be present in form of dispersion (note the difference solution - thermodynamically stable 1 phase system, dispersion 2 phase system, thermodynamically unstable).
As you can read in many discussions here on Researchgate - spectra will depend on size distribution of particles.
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Hi, I'm looking for any sources like books, reviews, etc. that defines generally "Diffuse Reflectance Spectroscopy. I acknowledge any helps in advance.
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Little heavy in math, but the following article shows theoretical background of diffuse reflectance.
You can Google Kubelka-Munk theory and you will find tons of references you can use. The original Kubelka-Munk theory was published many years ago as follows.
Kubelka, P.; Munk, F. Ein Beitrag Zur Optik Der Farbanstriche. Zeitschrift für Technische Physik 1931, 12, 593-601.
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I have reflectance spectra of a sample. R(w) (reflectance in wavelength 400-1000nm).
in keramers kroning analysis of the reflectance spectra, there is a shift phase integral:
w/pi(Int(ln(R(w))-ln(R(w')) / w^2-w'^2))dw)
I have R(w) but dont know what R(w') is.
Would you please somebody guide me, I interuppted in this part for MATLAB code write.
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Dear Afshan,
please compare the formula in your question and that in the reference . They are different. In the reference in the integral R(w) is substituted by R(w dash) such that one can one can get phi(w) at a given w while integrating over R(w).
Best wishes
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Please can you suggest to me more about the purpose of direct and indirect band gap.
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for a new material how can find that its band gap is direct or indirect?
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I cannot understand the difference between radiance and reflectance when measuring vegetation indices like NDVI.
I checked the definitions of Radiance and Reflectance - radiance is the radiation reaching the sensor and reflected by the surface whereas reflectance is the ratio of radiation striking the surface to the radiation reflected by the surface.
As far as I read, its better to calculate indices using surface reflectance values. Radiances are not suitable because they can be inaccurate due to atmospheric effects until the radiation reaches the sensor.
My question is, even if there were no atmospheric effects, how can vegetation index values calculated from radiance be similar to values calculated from reflectance? The two seem to be different things from their definitions. I would assume we would get highly varying vegetation index values.
So how is it still acceptable that people dont bother to convert radiances to reflectances before calculating vegetation indices?
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Hi Salman,
Even if in general is much convenient to use reflectance at the top of the canopy to better normalize atmospheric effects, it is not always needed. It could depend on what is the use of the NDVI.  For instance, if you want to make a regression with ground information using high resolution data (eg, Landsat), to use a NDVI _rad is perfectly valid. However, if you want to use NDVI for multitemporal estudies  to assess for instances changes in the vegetation canopy, you must use NDVI_ref to assure that observed changes are no affected by atmospheric effects.
Regards,
Fernando
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The Labsphere's Spectralon is widely used as a reference when doing spectral measurements. It is close to Lambertian surface but not ideal Lambertian surface, so when doing photometric measurements, the reflectance dependency on emission angles should be corrected.
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Hi Yazhou,
See attached, a part of my experimental data, corresponding to previous discussion.
You can invert, smooth, parametrize (or whatever) these experimental data.
Be careful that even if spectralon is a theorical reference, real material can be deteriorated getting used and aged. In other words, my spectralon is not exactly your spectralon.
This is the best I can do to answer.
Best regards.
亲切
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When the absorbance spectrum is recorded, it is found to be the same as that obtained from diffuse reflectance spectra after performing Kubelka Munk transformation. So, what is the advantage of kubelka munk over absorbance?
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Sorry to say that, but you compare apples and oranges. Absorbance does not refer to a particular measurement method. Correspondingly there exist transmittance absorbance (-lg T), reflectance absorbance (-lg(R/R0) etc. relating to the method of measurement. Please be more specific in your question and let us know from which method of measurement the absorbance derives.
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formula for conversion of OLI data from DN to reflectance?
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Can someone diffuse the mist surrounding this issue in my mind: how does one convert ToA reflectance to surface reflectance?
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I want the wavelength at each band of ROSIS sensor. it has  115 spectral bands. I dont know how to extract the wavelength at each band. ??
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thank you sir
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The synthesized materials are powders and thus diffuse reflectance was run rather than absorbance. I need to draw up Tauc plots to obtain the band gap. However, I have been struggling with the conversion of my data to the Kubelka-Munk graphs.
I have also tried to download UVProbe software but was unsuccessful.
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Thank you !
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I want to calculate the percentage content of water/ moisture present in human hair through Near Infrared Spectroscopy. any addition method has to be applied after spectra determinations to calculate exact / approximate water content ? 
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If they dont describe the exact amount of moisture content, then what information/ parameter do we get from NIR for hair fibres? is it possible to determine the same from any other technique ?
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now i am doing my project based on the abortion of materiel (that material like sand witch modal that means three materials in three layers, i want individual absorption of materials), how to calculate scattering of light, problem is i am doing nano meter range, i want accurate absorption of light in material,excluding scattering losses
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your point is not clear
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Dear all!
I am trying to characterize the surface reflectance of a thick semiconductor (i.e. transmission experiments are not applicable). As the sample is mounted in a cryostat I have no direct access and an integrating sphere cannot be used. Under these circumstances, what is a good way of measuring the surface reflection for extraction of the band-gap of the material (visible region)?
Thank you all in advance for your time and assistance!
Best,
Chris 
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Dear Christoph,
I am happy if it helped a bit.
Petr
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Hi,
Can I use MODIS corrected reflectance (true color) obtained from Worldview to track turbidity front? I do not want to know the concentration, only the position and area. Instead this, do I have to process the image from ocean color page?
Thank you in advance.
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Recently,I am studying on the influences about IR light to human beings. Except the absorption curve about human body to IR light,any related information is well and needed.
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The absorption of different constituents of human tissue has been extensively studied and many variations of the following graph can be found in literature and a quick google search.
Describing the interaction of light with skin is a complex challenge given the different interactions light has as a function of wavelength with different biological molecules. The low absorbance of NIR wavelengths as shown in the above link gives rise to the use of NIR in biomedical photonics. 
The following paper may be of interest if you haven't already seen it
Do you have a particular application in mind? For laser ablation you might want specific but high absorbance, whereas for imaging you will want low absorbance. 
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I fabricate a silicon nanocone array and I want to measure reflectance spectrum but I don’t know exactly what to do. In order to measure the reflectance spectrum, the reference spectrum must be measured. To do this, I can use two kind of standard mirrors, Al mirror (specular) and PTFE mirror (diffuse). But I do not know what standard mirror I have to use for reference spectrum measurement. For this measurement, I use Reflection probe and 10X objective (dimension of nanostructure is 200µm). Could you please guide me how I can measure reflectance spectrum in the reflection geometry from my nanostructures?
I calculate the Reflection spectrum using equation which is attached.
  Is it right? 
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 Dear Leila,
Maybe you misunderstood Vladimir's suggestion  to measure reflection from polished side of a Si wafer and to use it as reference. Use the formula you gave above with the same mirror to measure R of Si and compare your results with the literature data for Si. If you get right result for Si, then your simulation for nanostructure is wrong. If the result for Si is wrong, then check your experimental setup. Use metallic mirror. Deposited aluminium layer will be OK. Use a collimated beam with diaphragms to avoid different angles of incidence. Also you can use a beam splitter to achieve normal incidence. Measure reflection from the mirror and from the sample with the same slit width of the monochromator, only changing accumulation time (or amplification) if necessary  to avoid saturation of the detector. Then normalize signals from the sample, mirror and background to the same amplification (or accumulation time). Use your formula. Also, be concerned about polarizing effect of your momochromator grating if the incidence angle is not normal or if your nanostructure is birefringent.  Use a depolarizing  wedge.
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I have done a number of reflectance spectroscopy studies using both a PIMA and more recently the Terraspec to study alteration minerals for epithermal deposits and geothermal systems. Both have smectite, illite-smectite, illite with variable chlorite, calcite and kaolinite. In these studies I have calculated various spectral parameters derived from both reflectance and hull quotient corrected / continuum removed spectra. Curiously, the calculated H2O/Al-OH depth ratio  for the epithermal hosted in andesite for reflectance spectra show a better match with XRD results then the hull. However the opposite seems to be the case for the mostly rhyolite hosted geothermals. The shape of the hull differs between the two and it appears that for andesite there is typically a downward slope between 1900 and 2200 nm, whereas for the geothermal this interval is fairly flat / though the overall profile from 1200 to 2500nm is often convex. What is the cause of the continuum shape?
I should add, that the andesites are typically intensely altered and thus pale cream, white to pale - medium green / depending on chlorite content. Altered rhyolite from the geothermal shows the same range of colours.
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I am using cary 100 UV-VIS diffuse reflectance spectroscopy with 70mm integrating sphere.when I place the standard in the sample port and measure the reflectance the value I am getting is around 40%.
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It's ok since ther is incomplete light collection of light even by integrating sphere. You will get 100% after baseline recording. The reflectsnce of your samples will then calculated relative to your standard.
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I am working on rare earth metal perovskite photocatalysts. I want to calculate their band gap using the data from their reflectance spectrum.
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Dear Dr. Mahdi Karimi-Nazarabad
Assalamu alaikum 
Have a nice day and good times
Experimentally, You can get  the value of Eg by usually use the Tauc relation, which is given by this equation:                                
 αhν = A (hν - Eg )n
where α is absorption coefficient given by                
α = 1/t  ln [(1-R)2 / T]
where t  is the sample thickness, T and R are the transmission and  reflection, while  (hν) is the photon energy, where:
hν(eV) = 1240 / [incident wavelength (nm)]
If you plot a graph between (αhν)1/n  versus (hν), then you can get a straight line. This line intersects the X-axis at (αhν)1/n = 0 . The values of Eg have been estimated from this intercept.  The value of n is dependent on the electronic transition type. Where:
n=1/2 for direct allowed transition,
 n= 2 for indirect allowed transition, 
n=3  for direct forbidden transition and
n=3/2 indirect forbidden transition. You should try to select the suitable n according to your samples and their preparations.
The appended papers may help you; they are examples of direct and indirect allowed transitions.
Good luck
Your,
Ahmed Saeed Hassanien
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I'm just wondering whether there should be a difference in spectra of the same sample taken with the same equipment but in different modes of light transmission say one in reflectance and the other in transmittance but with the same light source! I will appreciate any little explanation in addition to answering this question. Thank you in advance.
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A couple of reflectance and transmittance spectra from the same sample can be found in the linked publication (calculations based on Fresnel's equations). There are definitely some differences...
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I am able to convert wavelength(nm) values to photon energy(eV) but I could not find out how to draw Tauc Plot from these values (i.e., reflectance and photon energy)
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Dear colleague Yeswanth Rayapati
Have a nice time and good day.
Herein fined all what you need about optical properties from A to Z. in details including the direct and indirect transition akso the references are included.
Due to the format of the Equations, it is included in the attached file so check the Eq. No. the see it in the attached file.
First you measure transmittance, T reflectance, R and/or absrobance using any spectrometer. 
If your spectrometer is not calibrated so you need to  calibrate your measured parameters otherwise go to step 2. Herein fined how to calculate the optical gap and constants of the film also the references are mentioned and all you need to overcame the all problems of optical properties [five items]. Due to the format of Equations it is attached in a separate file, just you know the equation number please check it through the attach file.
1- How to calculate the correction of T and R?
The reflectance was measured at normal incidence with an aluminum reference mirror. The absolute values of  transmittance, T and reflectance R of the substrates after correcting the  are given by [[**]A. A. Sagade,  R. Sharma, Sensors and Actuators B: Chemical, 133 (2008) 135-143 [**] M. Dongol, M. M. El-Nahass, A. El-Denglawey, A.F. Elhady, A.A. Abuelwafa. Current Applied. Physics 12 (2012) 1178.]
Equation No.……………………………...... (1)
Ift and Iq are the intensities of the light passing through the film-quartz system and the reference quartz, respectively, and Rq is the reflectance of quartz. In addition, if the intensity of light reflected from the sample mirror reaching the detector is Ifr and that reflected from the reflectance reference mirror is Im, then
Equation No.…………………… (2)
Ifr is the intensity of light reflected from the sample reaching the detector and Rm is the mirror reflectance.
T and R spectra were performed on thin film samples with single face. Extinction coefficient, k and refractive index, n were calculated using T, R and thickness d taking into account the experimental error of   the film thickness. T and R.
2- How to calculate  Absorption and extinction coefficient?
T, R and d are used to calculate the absorption coefficient, α
according to [[**]A. El-Denglawey, M. Dongol, M.M  El-Nahass, J. Lumin 130 (2010) 801.]:
Equation No.………………………….…….…… (3)
α is given by:
Equation No. …………………………………… (4)
The calculated α is included within high absorption region (α ≥ 104 (cm)-1).  
Extinction coefficient, k of TiO2 film is calculated by using:
 
Equation No. ……………………………………….…. (5)
3- How to calculate  Optical gap?
            An absorption edge of semiconductors corresponds to the threshold of charge transition between the highest nearly filled band and the lowest nearly empty band. According to inter-band absorption theory, the film’s optical gap can be calculated according to [[**]J. Tauc (Ed.). Amorphous and Liquid Semiconductors, Plenum, New York, 1976].
 
Equation No.…………………………. (6)
 A is a parameter of transition probability, it measures the disorder of material 
A = 4πσmin / nc∆E, Where  σmin is the minimum metallic conductivity, n is the refractive index, c is the light-velocity, and  ∆E = ∆Ec - ∆Ev   represents the  band tailing
[[**]M. M. El-Nahass, M. H. Ali, A. El-Denglawey Trans. Nonferrous Met. Soc.     China 22(2012) 3003−3011].  
is the optical gap of the material, hυ is the incident photon energy and r is the transition coefficient. The reported values of r are 2 for the measurement of indirect optical gap and 1/2 for direct optical band gap.
4- To determine the value of r plot the relation.
In case you know the value of Eg from the literature you can use:  ln (αhυ) = ln B+ r ln(hυ- Egopt) and find the value of r from the slope of the line for Ex.
 May you have both direct  and indirect band gap
The indirect optical gap, is evaluated by extrapolating the straight line part of (αhν)1/2 curves with energy axes (hυ) i.e (αhυ)1/2 = 0  according to eq:
Equation No.……………………………. (7)
Direct optical gap,  is evaluated by extrapolating the straight line part of (αhν)2 curves with energy axes (hυ) i.e (αhυ)2 = 0  according to eq:
Equation No.……………………………. (8)
Both direct, and indirect, optical gaps of TiO2 films may be found.
OR
to find the value of r the relation between (αhν)^1/r and incident energy (hν) for all values of r should be figured. The value of r which release a straight line represent the value of r and the electronic transition type.
5- How to calculate refractive index and dielectric constant?
Both R, and k at different λ were used to calculate refractive index, n according to:
[[**] T. S. Moss. Optical Process in semiconductor. Butter Worths, London, 1959.]
Equation No.     ………………………….… (9)
The dispersion of refractive index of the films is analyzed by the concept of the single oscillator and can be expressed by the Wemple–DiDomenico (WDD) relationship[ [**][S. H. Wemple, M. DiDomenico. Phys. Rev. B 3 (1971) 1338-1351] as: 
Equation No.          ……………….(10)
 Eo is the single-oscillator energy and Ed is the dispersion energy which is a measure of the intensity of the inter-band optical transition, it does not depend significantly on the band gap. The oscillator parameters can be determined  by fitting a straight line to the experimental points according to [[**][A. El-Denglawey. J. Non-Cryst. Solids 357 (2011) 1757-1763].
Plotting  vs (hν)2 allows to determine the oscillator parameters by fitting a straight line to the experimental points. By extrapolating the linear part of WDD optical dispersion relationship towards the infrared spectral region (hν = 0), static refractive index n(0), could be defined by the infinite wavelength dielectric constant ε∞ or n(0)2,
The relation between the lattice dielectric constant εL, and the refractive index, n as
[[**] A. El-Denglawey. J. Non-Cryst. Solids 357 (2011) 1757-1763.]:
Equation No. ………………………………….(11)
where εL is the lattice dielectric constant, N/m* is the ratio of the carrier concentration to the effective mass, c is the speed of light, and e is the electronic charge, εo is the permittivity of free space. The linearity of the plots of n2 versus λ2, verifying of Eq. (11). The value of εL is determined from the extrapolation of these plots to λ2 = 0 and N/m* from the slope of the graph.
Please notice that there is a direct calculation of ( hu) by this relation using wave length only.
E= hu =1240/wavelength (nm). 
I wish that is useful and help you.
Don't hesitate to ask about any thing concerning optical, electrical and structural properties.
Good luck
Yours
A. El-Denglawey
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measured reflectance peak amplitude decreased, with compared to modeled spectra?
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If you talk about the specular reflectance, a common reason is surface roughness... to give a more extensive answer, we would need more information about what kind of sample you measure in what spectral range by what method and instrument etc....
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Hello,
I am confused about how to accurately find out the band gap of a semiconductor using diffuse reflectance curve. I have plotted the data but am bit doubtful about the tangent to be drawn. I am uploading curve and have followed two methods to find band gap using tangent. Please confirm the correct method.
Is the method in image B correct or in B ? If not then how do I proceed.
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why we draw tangent? what is the reason behind this??
i think at (0,0) absorption is zero?
and one thing more why we take 1/2 and 2 for direct and indirect band gap?
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Landsat products from TM or ETM+ i have been using for LULC change detection . but now a new surface reflectance product is available . Can any body suggest is best use ..???
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For any LULC change detection study, the primary objective amongst others is to identify the changes which have occurred over a particular area. Therefore the object of interest is to identify the changes in land cover/land use and not the changes caused by atmospheric or radiometric effects or any other artifacts. As you know, when a satellite looks down on the earth, it also looks through a column of atmosphere which in a way obstructs the field of view of the satellite sensor before it senses the objects on the surface of the earth. Surface reflectance products as the name suggests are already corrected for radiometric and atmospheric effects. These pre-processing (radiometric and atmospheric corrections) steps which you anyway would have done with a normal Landsat product for carrying out a LULC change detection study, is now already been done for you when you use a Surface Reflectance product.
As these Landsat Surface Reflectance products are provisional, I would suggest you to manually carry out pre-processing steps and then compare your results with the Surface Reflectance products. Also go through the product guides for details.
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I am carrying out a lab experiment to see the effect of dry and wet soil on Emitted Radiance. The results are anticipated to help develop an understanding of how soil moisture influences Geothermal anomaly detection in remotely sensed data. To determine the amount of moisture in a soil sample, standard gravimetric method will be followed and the ratio of water content to dry soil will be recorded in %. For the associated Spectral measurements a Fourier Transform Infrared (FT-IR) Spectrometer ( 2.5 to 16 µm ) will be used to retrieve the directional-hemispherical reflectance values and subsequently converted into emissivity using Kirchoff's law. Using emissivity and temperature the Emitted Radiance can be calculated for each soil type in dry and wet states using Planck's black body equation. Emissivity measurements are crucial for accurate land surface temperature estimation.
However, setting-up the experiment requires some careful considerations. For example, it is challenging to keep soil sample homogeneously wet at least as long as the measurements are taken before the top part of the soil dries up. One of the suggestions is to take the spectral and soil moisture measurements quickly to have a good estimation of the soil moisture at the top layer. Since the TIR measurements are restricted only to the top few micrometers/sub millimeters of the soil surface or otherwise known as the skin level, it is essential that the soil moisture measurements correspond to the TIR measurements.
Are there any alternative ways to do the same experiment? What other challenges can be expected?
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As I understand correctly, you want to depict SMC. You need to have soil moisture for suction or metrics. You need a Pressure Plate to measure soil moistures at different pressures (negative pressure=suction). From Field capacity moisture (pressure=-0.33 atm to PWP((permanent wilting point)=-15 atm). You need at least 10 points to suitable distribution along this suction ranges.   
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How can i get of the infrared spectra of semiconductor compounds.
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The best and most reliable way in my opinion is to measure the polarized IR-reflectance from a single crystal and to analyze these spectra by dispersion analysis employing suitable oscillator models. Thereby you not only get the dielectric tensor function, but also information concerning carrier density, oscillator positions etc.
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The wavelengths are 400 to 1000 nm.
I would like to know not the particle's absolute absorbance value just how they relate to each other; which of these particles reflect the most light.
is it  correct assumption that the bigger the area of the spectrum is the more löight is being reflexted 
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Dear Aras, the curve is like that, it is just flat at a certain wavelength range, higher values could be detected.
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Hi All, 
I have to set up a phantom study as well as an in vivo study for measuring light reflectance spectra of human tissue using diffuse reflectance spectroscopy technique.
I have to choose up to 4 wavelengths but not sure what wavelengths do I need to perform my experiments.
Need to be mentioned that data obtained from experiments will be used for validating numerical a light propagation numerical model (Monte Carlo).
As my second question, what difference does it make using a LED as a light source instead of laser?
Thank you very much.
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Hi Amir,
there is no simple answer to you question since any wavelength interacts with tissue. So if you do not kwow which physical effect you want to study. Diffuse Reflectance is usually due to body scattering. Scattering itselfe is dependent on the wavelength and the size of the targets (and other things, maybe have a look at wikipedia or a textbook). 
You should also consider absoption. If you choose a wavelength that is, e.g. stongly absorbed by water it migth not give you much signal in refectance.
As for the difference between lasers and LED, laser are basically strictly monochromatic, means emitt light with one exact wavelength, LED emitt ligth with an band of wavelengths, means a maximum wavelength and bandwidth.
Hope that gives you some directions.
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Could anyone help with the instrument using for reflectance measurement?
Our Lab has JASCO V-670 instrument and ISV-723 60mm integrating sphere.
But no one knows how to use those things..
And I want take reflectance spectrum using this instrument.
Please help me ;)
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Not to be confused with REFLECTIVITY - not my area of expertise
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I am trying to do a UV-Vis diffuse reflectance measurement using a Perkin Elmer Lambda 750 instrument. Do you have experience with the instrument set up, where and how to put the sample in the holders, what should be used for back ground correction.
I try but could not contact Perkin Elmer for a training.
I attached a photo of the sample compartment for your reference. Please advise!
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Hi,
If you want to use the integrating sphere, you might not need to do sample prep with BaSo4.
I have worked a lot with integrating and double-integrating spheres in general, and this is how it works.
In integrating sphere, one places a thin layer of sample in a glass/quartz cuvette such that it covers the sample entry port of the integrating sphere completely. Integrating sphere offers the option of measuring DIFFUSE reflectance/transmittance. For diffuse reflectance measurement, you allow the light beam to enter from the port almost at 180 degree to the sample port, such that the collimated light travels in a straight line in the integrating sphere and then falls onto the sample. As one can imagine, a portion of light falling onto the sample will get reflected back through refraction within the sample. And this will be the DIFFUSE back scattered light. This will fall onto the walls of integrating sphere and will homogeneously diffused by multiple reflections within the integrating sphere. And you will find a detector port in the integrating sphere so that you can collect the diffuse light in the integrating sphere onto the detector.
It is worth to look at some work published by Prof. Scott Prahl (father/inventor of this tech). http://omlc.org/software/iad/
One good reference to start with: http://omlc.org/~prahl/pubs/pdfx/pickering93a.pdf
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I have successfully synthesized my nanocomposites with different concentrations. For optical properties i have done Diffuse Reflectance Spectroscopy(UV-Visible). I observe reduction in the Reflectance as well as the band gap of the material as I increase the concentration of second material. So tell me the possible reasons why the band gap and reflectance changed?
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when you are adding some impurity into any material then it has its own energy states which you can call virtual states below or above the conduction band of host material
if the doping material has virtual states below the conduction band of host material then reduction in bandgap occurs
and vice versa.
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Actually I've got the DRS (diffuse reflectance Spectroscopy) results of my samples i.e. WO3 Nanoparticles, and I've applied Kubelka Munk function to get the band gap of my results but its much more than it is reported, the reported results of the band gap of WO3 is from 2.4 eV to 3 eV (max), so I want to know is kubelka-munk function the reliable method to find the band gap of materials?
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Astro, but the problem here is that we have nothing to  do with the tauc plot, because there is reflectance data against the wavelength... so we can not have tauc plot for these values, how can we varify the bandgap (Eg) with having reflectance spectra...I heard there're some more methods for finding the bandgap as well... is it right? If yes what are they? Dr. Roberto
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I have synthesis WO3 nanoparticles. I have characterize my material via DRS for optical properties but it has two peaks. What is the first peak is showing? I have attached a picture also. There are many formulas which can be used to analyze DRS, i.e. KMF, bulk munk and etc. Which one is the best? What kind of properties other than optical properties can be explained using DRS? Kindly attach Pdf files of DRS analysis of WO3 nanoparticles if someone have it.
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Diffuse reflectance accessories make the analysis of solid samples much easier instead of solutions (i.e. in UV-vis.) KMF is a very good tech to find the Energy band gap...
Here a file of Indium doped ZnO is attached that can help us understanding the DRS 
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I'm using RapidEye data to calculate vegetation indices from a cropped area. I'm interested in using this index which has an equation as fellows: 
( Red / Near Infrared ) / ( r680 / r800 )
It is clear that red and Near infrared as bands 3 and 5, respectively for RapidEye. But it is not clear what does r680 / r800 mean? I appreciate your assistance.  
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Thank you Riyad and Rajasheker. 
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I have images from a Specim SWIR terrestrial hyperspectral camera, and I have converted them to radiance.  I also have FODIS data, which can be used to convert to reflectance, I'm just not quite sure how to do this.  
image: n lines, 291 samples, 256 bands.
FODIS data: n lines, 1 sample, 256 bands.
Any suggestions would be greatly appreciated.
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Hi Lukas!
Consider the following:
Reflectance is equal to the ratio of the reflected radiance and the incident radiance. The SPECIM radiance measurements correspond to the reflected radiance, while the FODIS measurements to the indicent radiance. Thus, to estimate the at-sensor reflectance you have to calculate the SPECIM/FODIS ratio for each one of the available spectral bands. Moreover, because the FODIS measurements are point data, the same FODIS measurement will be used for all the samples of each SPECIM line.
It is important that you pay attention to the following points:
  • The retrieved reflectace values will still carry the atmospheric influence (i.e. using this method you will estimate the at-sensor directional reflectance and not the at-surface directional reflectance).
  • Before applying this method you have to correct the FODIS measurements for the roll, pitch and yaw movement of the aircraft.
  • the SPECIM and FODIS radiance measurement units should be compatible.
  • Be very careful if clouds where present during the image acquisition.
Hope this will help,
Panagiotis
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Does COMSOL have the same capabilities as the monte carlo method in modeling light-tissue interactions in terms of calculating and obtaining light distribution over the surface as well as inside the tissue in 3D?
Thank you.
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Hi,
Comsol cannot offer you the same accuracy as MC. The reason is obvious: Comsol can solve the diffuse approximation (DA) equation, which is valid only in high scattering media and far enough from the source. On the contrary, MC can provide results more or less equal to the radiation equation if enough photons are used.
Some more links for Comsol and DA:
Best regards
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I want to calculate Optical conductivity sigma(op). I have reflectance data of my samples. 
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Thank your for answer.
I want derivation of refractive index (n) 
Optical conductivity =  alpha x n x c/4pi
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We use a Xenon lamp, a monochromator, an integrating sphere and a photodiode to measure the total reflectivity of thin films (metallic, or organo-metallic nanocomposites thin films). I'm looking for a procedure (geometry configuration, reference measurements, data analyzis) to do a reliable measure.
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Hi,
regarding the reference measurement, there are two types of reference standards, specular reflectors like aluminum mirrors, and diffusive reflectors, for instance dielectric powders (BaSO4 is very common). It depends on your sample what is the right choice for you. In principle, it is desirable to have a standard whose reflection properties are similar to those from your sample. For instance, if you have a sample with a highly specular reflectance such as a thin metal film or a silicon wafer, a specular reflectance standard should be used.
Reference standards can be commercially purchased, but are quite expensive when they come along with a calibration certificate. A "low cost" solution is to use a sample with known optical constants as standard, for example a silicon wafer. The optical constants can be determined by an independent measurement such as spectroscopic ellipsometry. From the optical constants, the reflectance to be expected can be calculated using the Fresnel equations.
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My question is about how to convert the data to percentage or to value that has defined dimension. Also it is nice to be clear if those data could be compared to those from in-situ measurements. Up to now I could not find reference for usage of this product.
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Hi Hristo,
I have some experience in using the Landsat surface reflectance product, and have eventually validated this product over the urban coastal environment of Hong Kong, you can have a look in the attached publication.
Regarding the conversion of the surface reflectance product into percentage you can consult the LEDAPS SR product guide.
Majid
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I'm using uv-vis reflectance to investigate multilayer structure. The UV-vis light is normal inciedent. The reflectance v.s. wavelength data was than obtain and exhibited a curve with many oscillations. How to analysis/fit the curve to obtain the structural inforamtion, include layer thickness, wavelength dependent refractive index, or maybe layer roughness?
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Check for example the attached papers. There we studied in one case a film composed of several phases. Some information regarding them was extracted but layer thickness is not possible to calculate in cases like this using UV VIs as the refraction index would be the contribution of the each phase distribution in the film volume. In the other case we studied an copper oxide film over a metal substrate and we were able to subtract the contribution of each one and calculate thickness and n and k dispersion by the use of software SCOUT. For multilayer films I guess you could try SCOUT also (is not freeware) or software included in some apparatus to measure thickness (I remember that Ocean Optics have one), but a model of your system would still be needed to first guessing the optical parameters.
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When I calculate the optical gap of my thin films deposited on Corning glass via transmittance UV-Vis-NIR measurements , I find a different value than that I calculated via reflectance UV-Vis-NIR measurement.
I wonder what in the structure or the surface of the film has to be taken in consideration to make Reflectance measurements ????
Thank You
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For band gap calculation, you require transmittance as well as reflectance along with the thickness of the films. You can use Tomlin's equations for determining extinction coefficient and then Tauc's plot will give you reasonable perfect value of band gap.   
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We have recorded a Diffuse Transmission Reflectance spectrum by keeping the test sample in the entrance of the integrated sphere in %R mode and later converted it in K-M. What is the actual good practice? 
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It is ok but have you taken care to properly subtract the background and carry out the baseline correction to make it flat through zero?
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Fe(II) complex shows Spin State Cross Over (SSCO)phenomenon. Will it give reflectance spectrum corresponding only to its high spin state or only to its low spin state or simultaneously to both the states at SSCO temperature? Give argument/s.
SSCO
Manohar sehgal
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Reflectance (and more generally UV-Vis, IR and Raman spectroscopy) are routinely used to monitor Spin Crossover with temperature/light/pressure, since HS and LS spectra are different enough that you can see the variation. Reflectance is a quick way to follow the variation with temperature since you can do it on powder, using homemade setups that avoid the constraints of cryostats needed for high-performance UV-Vis spectrometers.
At any temperature you will have a mixture of x complexes in HS state and 1-x in LS state. The spectrum of the sample will be the sum of both. Inversely you can extract x from the spectra provided you have a reference. Difficult to do with reflectance and more generally UV-Vis given the broadness of the bands, easy with IR and especially Raman if you find markers specific to one spin state.
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Hi, I am a beginner in BRDF/Albedo research. And I need to draw a two dimensional plot revealing the relationship between "Bi-directional reflectance" and "view zenith/azimuth angle", just like a plot in the attached picture. Would anyone please tell me how to draw it, with a little bit of detail? Thank you so much!
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Hi,
why not using gnuplot ? For example :
set parametric
set isosamples 30 , 30
Rx(u,v)=cos(u)*cos(v)
Ry(u,v)=sin(u)*cos(v)
Rz(u,v)=sin(v)
brdf(u,v)= .......
Brdfx(u,v)=brdf(u,v)*Rx(u,v)
Brdfy(u,v)=brdf(u,v)*Ry(u,v)
Brdfz(u,v)=brdf(u,v)*Rz(u,v)
splot [-pi:pi][0:pi/2] Brdfx(u,v),Brdfy(u,v),Brdfz(u,v)
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Linear and nonlinear multivariate regressions
Soil spectroscopy
soil organic carbon
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Thank you very much Dr. Yarnold for your detailed answer and very interesting references as well. actually, I am asking about the method which maximizes the predictive accuracy and its package for R.
Best regards,
Said
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I have recorded FTIR spectra for my biological sample.
I would like to convert the spectra  to reflectance mode .
Is there any conversion formula ?
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If you're looking at diffuse reflectance, a typical conversion formula used is "Absorbance = Log(1/Reflectance). There are also some data processing software packages, e.g. Unscrambler X (Camo Software), which allow you to convert spectra between absorbance, transmission and reflectance units - though licenses can be a bit pricey
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How much more reliable is the comparison of transmission data and reflectance data for a  thin film of polymer coated on ITO/glass and Platinum respectively? 
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it is absorbance which the spectrometer records. Simultaneously it give transmittance spectra also which is related logarithmically to absorbance. In case of reflectance measurements there are only absorbance and reflectance values which we get. 
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Reflectance calculation.
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Actually the answer of "Can we calculate reflectance from transmission data?" is definitely "yes" in the case of transparent sample with smooth surfaces. For absorbing sample the answer also could be "yes". For example if the sample is thin film on known substrate someone can use transmittance data for determination of refractive index, extinction coefficient and thickness of the film and then using the already obtained data to calculate reflectance spectra by well known equations. I personally prefer matrix transfer formalism.
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I have a two dimensional feature space plots for spectral reflectance in ERDAS imagine
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Great webtool although I am looking more to export the 2D spectral feature plots from ERDAS imagine and provide the output on a graph indicating the measure of DN along the axis.
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I have data for reflectance vs wavelength by uv vis nir. I want to calculate R∞ for our sample and after that I want to calculate K-M (Kubelka-Munk) function (f(R∞)).
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Apply the following relations as required with the experimental data.
[I] The well known relation is:
R+A+T=1.
Because the sum of Reflectivity (R), Absorbance (A) and
Transmittance (T) is equal to one.
[IIKnowing α (the optical absorption coefficient ), calculate the thickness (t) of the optical material by applying the relation:
α. = 2.303A/t
Or
If thickness of the material is given, calculate A, the absorbance.
Or
Still there is another way to calculate α if band gap of the material is known as:
α = (h. ν -Eg) ^1/2.
[III] Again, knowing α, calculate k; the extinsition coefficient as:
k= α λ/4π .
I[V]T is exp’tlly known.
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We have reflectance data of multilayer oxide films in which metal film is sandwiched. We want to extract refractive index values of the oxide layers. Is this possible?
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thanks Saumya
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The UniSpec-SC is usually used in plant leaf measurements but if it is able to measure Total Reflectance it is possible to use it in any surface, or is it calibrated exclusively to plants? If so, could I adapt it somehow to measurements of animal skin?
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Many thanks Carl, this was really useful!
I will check the bibliography that you suggest!
Thank you!