T. Yanev

Bulgarian Academy of Sciences, Ulpia Serdica, Sofia-Capital, Bulgaria

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Publications (25)6.67 Total impact

  • M.G. Tsaneva · D.D. Krezhova · T.K. Yanev
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    ABSTRACT: A statistical model is proposed for analysis of the texture of land cover types for global and regional land cover classification by using texture features extracted by multiresolution image analysis techniques. It consists of four novel indices representing second-order texture, which are calculated after wavelet decomposition of an image and after texture extraction by a new approach that makes use of a four-pixel texture unit. The model was applied to four satellite images of the Black Sea region, obtained by Terra/MODIS and Aqua/MODIS at different spatial resolution. In single texture classification experiments, we used 15 subimages (50×50 pixels) of the selected classes of land covers that are present in the satellite images studied. These subimages were subjected to one-level and two-level decompositions by using orthonormal spline and Gabor-like spline wavelets. The texture indices were calculated and used as feature vectors in the supervised classification system with neural networks. The testing of the model was based on the use of two kinds of widely accepted statistical texture quantities: five texture features determined by the co-occurrence matrix (angular second moment, contrast, correlation, inverse difference moment, entropy), and four statistical texture features determined after the wavelet transformation (mean, standard deviation, energy, entropy). The supervised neural network classification was performed and the discrimination ability of the proposed texture indices was found comparable with that for the sets of five GLCM texture features and four wavelet-based texture features. The results obtained from the neural network classifier showed that the proposed texture model yielded an accuracy of 92.86% on average after orthonormal wavelet decomposition and 100% after Gabor-like wavelet decomposition for texture classification of the examined land cover types on satellite images.
    No preview · Article · Oct 2010 · Advances in Space Research
  • I. Iliev · D. Krezhova · T. Yanev · E. Kirova · V. Alexieva
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    ABSTRACT: The chlorophyll fluorescence in response to salinity stress of soybean plants in spectral range 650-850 nm and slow transient fluorescence kinetics were investigated using remote sensing techniques. The soybean plants were grown under controlled conditions as water cultures on nutrient solution of Helrigel. Salinity was performed at the stage of 2<sup>nd</sup> to 4<sup>th</sup> trifoliate expanded leaves by adding of NaCl in the nutrient solution at concentrations 40 mM and 80 mM. The chlorophyll fluorescence was registered by a multichannel fiber optic spectrometer USB2000 working in time-acquisition mode. As a source of actinic light, a light emitting diode with the maximum of the light output at 470 nm was used. The fluorescence spectra were registered subsequently in time at every 2 second. At least 40 spectra from each soybean leaf were obtained; the leaves being taken from 20 control plants and 20 plants treated with two NaCl concentrations. Measurements were conducted on the 14<sup>th</sup> day after treatment. Several indices such as fluorescence spectra area, halfwidth of the fluorescence spectral curve, and wavelength of spectrum maximum were used to characterize the differences between the normalized fluorescence spectra of leaves of control and treated plants. The Student t-criterion, discriminant analysis and derivative analysis were applied to estimate the statistical significance of the differences between the average values of the indices. The results revealed that the low NaCl concentration led to salinity tolerance while the high NaCl concentration caused salinity stress in the soybean plants.
    No preview · Conference Paper · Jul 2009
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    D.D. Krezhova · A. H. Krumov · T.K. Yanev
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    ABSTRACT: We present results from examination of the dynamics and spectral distribution of the solar radiation reaching the Earth's surface during the total solar eclipse on March 29, 2006. The solar spectra were recorded using a multichannel spectrometer OCEAN USB2000 in 2048 spectral channels in the spectral range 350-1000 nm at a spectral resolution (halfwidth) of 1.5 nm. The spectral measurements were carried out between the 1st and 2nd and the 3rd and 4th contacts of the total solar eclipse from an observation point situated on the Mediterranean Sea coast, Antalya region, Turkey. The spectral data were evaluated using statistical methods such as the Student's t-criterion and others. The changes in dynamics of incident solar radiation intensity before and after eclipse totality were found to correlate (R[approximate]0.998) with the changes during the total Sun's eclipse on August 11, 1999, observed from an observation post on the line of totality situated on the Black Sea coast on Bulgarian territory. The changes in solar radiation measured before and after totality, within the absorption bands of water and oxygen, as well as along the spectra envelope, show statistically significant differences, which point to an unstable terrestrial atmosphere. Images from concurrent videometric observations proved that fine cloudy structures have appeared after totality in front of the solar disk.
    Preview · Article · Feb 2008 · Journal of Atmospheric and Solar-Terrestrial Physics
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    ABSTRACT: Remote sensing studies on the spectral reflectance of natural formations – rocks, products of different physical and chemical processes in the Earth’s crust and its surface – are reported. Based on spectral reflectance characteristics (SRC) of selected representative rocks with different structure, mineral composition and colour characteristics – sedimentary (psephite-conglomerate) and metamorphic (kyanite schist) – and by applying statistical and deterministic methods the rock types and the main rock-forming components were discriminated. The spectral data were obtained in laboratory using a multichannel spectrometer developed in STIL-BAS, which delivers data in the spectral range 480–810nm.The a priori mineralogical information about the specimens studied, the actual SRC data, affine and perspective transformations of the colour coordinates of SRC were all utilized to perform a primary classification of the main constituents of the specimens. Cluster analysis was applied and its results were used to design the necessary grouping variables as required for the implementation of linear discriminant analysis. The discriminant functions were constructed from the SRC values for a selected set of wavelengths and of transformed data. Classification of the main ingredients and the rock types were obtained. The proposed novel approach to the spectral discrimination of main rock-forming components is believed relevant for predictive classification of other specimens of rocks through discriminant functions.
    No preview · Article · Dec 2007 · Advances in Space Research
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    ABSTRACT: Results from a remote sensing study of the leave spectral reflectance of pea plants (Pisum sativum L. cultivar Scinado) treated by the photosynthetic herbicides fluridone and acifiuorfen are presented. According to the mode of action, fluridone belongs to Fl (photobleaching) group of herbicides, and acifiuorfen -to the group E as classified by the Herbicide Resistance Action Committee. The pea plants were grown hydroponically in a growth chamber in a nutritious medium to which the herbicides were added at two low concentrations (1 muM, 0.1 muM for fluridone, and 25 muM, 2.5 muM for acifiuorfen). The high-resolution spectral data were obtained in the visible and near infrared ranges of the spectrum (450/850 nm) using a USB2000 fiber optic spectrometer at a spectral resolution (halfwidth) of 1.5 nm. After data analysis, optimal spectral intervals for evaluation of the herbicide action were specified. The changes occurring in the spectral reflectance of the pea plants were assessed in four intervals: 520/580 nm (region of maximal reflectivity of green vegetation), 640/680 nm (region of maximal leave absorption), 690/720 nm (red edge region), and 720/770 nm (near infrared region) using the t-criterion of Student and linear discriminant analysis. Statistically significant differences were found between the spectral reflectance data of leaves of control and treated with herbicides plants at a significance level p<0.05 for the two fluridone concentrations and for 25 muM concentration of acifiuorfen. The applied approach provides fast and reliable remote sensing of plant response to the environment.
    Full-text · Conference Paper · Jul 2007
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    D. D. Krezhova · T. K. Yanev · A. H. Krumov
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    ABSTRACT: Results from videospectrometric investigations of the solar radiation during the total solar eclipse on 11 August 1999 in the territory of Bulgaria are presented. The spectral distribution and integral changes in the solar radiation reaching the Earth's surface as well as images of the Sun's disk were registered from an observation post on the line of totality situated on the Black Sea coast. The solar radiation was measured by means of a high-resolution multi-channel spectrometer and a photometer. Black and white images of the Sun's disk were taken using a television CCD-camera through a neutral filter. The examination of the solar radiation dynamics revealed presence of fluctuations in the recorded spectral distributions before and after the eclipse totality expressed in a weak redistribution of the solar energy in the spectral range (480÷810 nm) in the limits of 1÷2%. The joint processing of spectrometric, photometric and videometric data disclosed a high correlation (R ≥ 0.9985) between the integral and spectral changes of solar radiation with time as well as a concomitant correlation between the solar radiation intensity and the changes in the area and the brightness of the unshaded part of the solar disk in the time interval before and after the totality. The applied statistical method (Students' t-criterion) proved statistically significant differences at a probability level of p
    Preview · Article · Jan 2007
  • D. Krezhova · V. Alexieva · T. Yanev · S. Ivanov
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    ABSTRACT: Results from a remote sensing study of spectral reflectance of leaves of pea plants Pisum sativum L treated by the herbicides atrazine 2 4-D glyphosate fluridone and chlorsulfuron are reported According to the classification of the Herbicide Action Committee reflecting their mode of action they belong to different groups photosystem II bloker - C1 atrazine synthetic auxins - O 2 4-D inhibition of EPSP synthase - G glyphosate photobleaching - F1 fluridone and inhibition of acetoctate synthase - B chlorsulfuron The plants studied were grown hydroponically in a growth chamber in a nutritious medium to which every herbicide was added at three low concentrations 1 mu M 0 1 mu M and 0 01 mu M with respect to the field dose applied in the agricultural practice The spectral measurements of the leaf spectral reflectance were carried out in laboratory using a multichannel spectrometer in the visible and near infrared regions of the spectrum 480 div 810 nm Data was registered in 128 channels at a high spectral resolution of 2 6 nm halfwidth and a spatial resolution of 2 mm 2 The reflectance spectra were obtained from the leaf-reflected radiation referenced against a standard white screen To assess the changes arising in the leaf spectral reflectance under the herbicide action the developed by us approach based on discriminant analysis and other statistical methods was applied The spectral reflectance characteristics SRC were investigated in three spectral intervals 520 div 580 nm region of maximal
    No preview · Article · Jan 2006
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    ABSTRACT: Based on high resolution leaf spectral reflectance data a new technique was developed and applied to detect damages of agricultural plants under the action of low intensity stress factors (herbicides) which at very low concentrations could not be established by the standard biochemical and biometric techniques. Results are presented from a remote sensing study of the peculiarities of the leaf spectral reflectance of pea plants (Pisum salivum L.) treated with atrazine and 2.4-D (2.4 - phenoxyacetic acid) at three low concentrations (0.01 μM, 0.1 μM and 1 μM, respectively 2.15, 21.5, and 215 μg/l for atrazine and 2.59, 25.9, and 259 μg/l for 2.4-D) as compared to the field dose of these herbicides commonly used in the agricultural practice. The physiological status of the plants was assessed using biometric and biochemical parameters such as length, fresh weight, dry weight and electrolyte leakage. The high-resolution spectral data were obtained using a multichannel spectrometer in the visible and near infrared ranges of the electromagnetic spectrum in 128 channels at a spectral resolution (halfwidth) of 2.6 nm. Using the technique which employs discriminant analysis and other statistical methods we established the presence of statistically significant differences in the arising variations of the leaf spectral reflectance characteristics between control and treated plants in the green (520+580 nm), red and near infrared (690+800 nm) ranges of the spectrum.
    No preview · Conference Paper · Jul 2005
  • T. K. Yanev · B. J. Choudhury · D. N. Mishev
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    ABSTRACT: More than one spectral classes are usually found within a pixel when measuring the spectral reflectance (the spectral reflectance coefficients (SRC) in particular) of natural formations in the visible (VIS) and near infrared (NIR) spectral ranges. The spectral mixture “soil-vegetation” is a typical example. The decomposition of this mixture is strongly impeded because only the mixture SRC are usually available, the soil SRC and the vegetation coverage coefficient p not being known in advance. This is especially true for remotely sensed data in field experiments. Under the assumption that the soil SRC are a linear function of the wavelength two SRC transforms were defined and studied in previous papers of the authors. The second transform is the θ coefficient, which is free of the unknown linear soil component as well as of the unknown coverage coefficient p. In previous studies of the authors θ was examined in the case when the soil SRC may be approximated by one straight line. In this work, θ was obtained and studied for soil types that may be satisfactory piece-wise approximated by two different crossing straight lines within the VIS and NIR ranges. Thus, the θ coefficient may be employed to eliminate the unknown soil SRC from the measured mixture SRC in the case when the soil SRC are nonlinear wavelength function which may be fitted by two straight lines. Examples of USA and Bulgarian soil types are given in the study, which meet this requirement.
    No preview · Article · Feb 2005 · Acta Astronautica
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    D Krezhova · S Pristavova · T Yanev
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    ABSTRACT: Results from a remote sensing study on the spectral reflectance of intermediate igneous rocks in the visible and near infrared spectral ranges of the electromagnetic spectrum are presented. The spectral data were obtained in laboratory by means of the multichannel spectrometer of high spectral and spatial resolution which was developed by scientists from STIL – BAS. Spectrometric measurements were carried out on characteristic intrusive and volcanic representatives of intermediate rocks that were generated in different depth facieses. Specimens of diorite and andesite, monzonite and latite, and syenite and trachyte were put side by side. To discriminate the rock specimens by spectral features a method based on statistical techniques such as Student's t-criterion, cluster analysis and discriminant analysis was developed and applied to their spectral reflectance characteristics. There were found statistically significant differences between the averaged spectral reflectance characteristics of the classification groups of intermediate basic rocks as well as between the spectral reflectance characteristics belonging to a classification group. By spectral features there were discriminated at a statistically significant level of confidence the main rock-forming minerals. The investigations were aimed as well to help in revealing the influence of texture peculiarity and variations of the chemical and mineral composition of rock specimens on their spectral features. СПЕКТРАЛНИ ДИСТАНЦИОННИ ИЗСЛЕДВАНИЯ НА ИНТРУЗИВНИ И ВУЛКАНСКИ МАГМЕНИ СКАЛИ Д. Крежова 1 , С. Приставова 2 , Т. Янев 1 1 Централна лаборатория по слънчево-земни въздействия (ЦЛСЗВ), БАН, София 1113; krezhova@stil.bas.bg 2 Минно-геоложки университет "Св. Иван Рилски"; София 1700; stprist@mgu.bg РЕЗЮМЕ. Проведени са експерименти за дистанционно изследване на отражателната способност на магмени скали, формирани в различни дълбочинни фациеси. Подбрани са образци на характерни интрузивни и вулкански представители на среднобазични магмени скали:с нормална и повишена алкалност: диорит -андезит; монцонит – латит и сиенит -трахит. Спектралните данни са получени в лабораторни условия с многоканален спектрометър с високи спекттрална и пространствена разделителни способности във видимата и близката инфрачервена области на електромагнитния спектър. За разграничаване на скалните подкласове по спектрални признаци е приложена разработена от нас методика. Върху данните за отражателната способност на скалите (спeктрални отражателни характеристики) са приложени статистически методи (t-критерий на Стюдънт, клъстерен анализ, дискриминантен анализ и др.) за установяване на статистическата достоверност на разликите на осреднените спектрални отражателни характеристики в избрани дължини на вълните, равномерно разпределени в изследвания спектрален диапазон. Изследванията са насочени и към установяване на зависимостите на спектралните признаци от текстурните особености и вариациите в химичния и минерален състав на изследваните образци, както и за използване на спектралните признаци за разграничаванито им.
    Full-text · Article · Jan 2005
  • T. Yanev · D. Krezhova

    No preview · Article · Jan 2004
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    ABSTRACT: A remote sensing spectrometric method for aerospace and ground based research was developed and laboratory tested to provide reliable information for discrimination of basic classes of natural objects and identification of their diversity and status. Spectrometric investigations under laboratory conditions were carried out on rocks, products of different physical and chemical processes in Earth's crust and its surface. Natural rock surfaces of basic genetic types of rocks, such as igneous (granite, quartzmonzonite, rhyolite), sedimentary (psephite - conglomerate) and metamorphic (kyanite schist) with various mineral composition, were investigated by their spectral reflectance characteristics (SRC) in the visible and near infrared ranges of the electromagnetic spectrum. SRC were obtained by means of the multichannel spectrometric system ``Spectrum 256'' developed by scientists from STIL and used for more than 12 years onboard the manned space station MIR. ``Spectrum 256'' operates in the spectral range 450div 850 nm in 256 or 128 spectral channel mode at 1.3 nm or 2.6 nm channel halfwidth, respectively. Adapted for laboratory measurements, the system provides a spatial resolution from 2 mm2 to 10 mm2. SRC from adjacent 40 pixels per sample taken along horizontal profiles were recorded on the average. A preliminary classification of the spectral subclasses of the primary rock-forming minerals in the samples was made using the projective transform of measured SRC as well as the SRC color coordinates and taking into account the corresponding mineralogical information. The results were utilized to design the grouping variables necessary as an a priori input information for the application of linear discriminant analysis over the training set of rock samples. Then the discriminant functions were obtained through the measured SRC for selected subsets of wavelengths and applied for statistical predictive classification of new rock samples by means of the discriminant functions. The selection of the subsets of wavelengths was performed through the Student's t-criterion - these wavelengths were chosen for which the mean SRC of the preliminary spectral subclasses differed at minimal p value of the t-criterion. This approach may be applied to discriminate between classes belonging to any other set of natural formations characterized by SRC.
    No preview · Article · Jan 2004
  • I M Stoilova · T K Zdravev · T K Yanev
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    ABSTRACT: Sleep problems have been observed during many of the space flights. The existence of poor quality of sleep, fatigue, insomnia or different alterations in sleep structure, organization and sleep cyclicity have been established. Nevertheless results obtained from investigations of human sleep on board manned space vehicles show that it is possible to keep sleep patterns related to the restorative and adaptive processes. For the first time in the frame of the "Intercosmos" program a multi-channel system for recording and analysis of sleep in space was constructed by scientists of the Bulgarian Academy of Sciences and was installed on board the manned Mir orbiting station. In 1988 during the joint Bulgarian-Russian space flight continues recording of electro-physiological parameters necessary to estimate the sleep stages and sleep organization was made. These investigations were continued in next space flights of different prolongation. The results were compared with the findings obtained under the conditions during the pre- and post-flight periods.
    No preview · Article · Feb 2003 · Advances in Space Research
  • D. Mishev · T. Yanev
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    ABSTRACT: The number of non-operating objects in a drift orbit increases and becomes a troubleshooting space debris problem. The solution of it would possibly be simplified if, by means of some discriminative procedure, they can be grouped with respect to their catalogued orbit elements. In a previous work of the authors an apogee-perigee contrast coefficient (APCC) was used as a transform instrument to detect specific clusters of approximately 340 debris objects (updated to 2001) in a drift orbit. It was proved that objects which are strictly linearly correlated in the coordinate system " perigee mean deviation from the geostationary altitude (rp) - apogee mean deviation from the geostationary altitude (ra) ", are located on the arms of a two-arm hyperbola in the coordinate system APCC - rp , where APCC = (ra - rp.) / (ra-+ rp.). This transform reveals possibilities new clusters of objects to be detected in comparison with the linear regression (ra,,rp.). In this work it was proved that the transform APCC distributes such objects into two groups: all objects for which |ra| > |rp| are disposed on the hyperbola arm, which is determined by APCC > 0 and vice versa: all objects for which |ra| < |rp| are disposed on the hyperbola arm, which is determined by APCC |rp| and |ra| < |rp| would possibly be specific indicators for some common features of launching, exploiting and deorbiting of the objects in a drift orbit which satisfy these inequalities. Local clusters of objects on one and the same of the hyperbola arms are not excluded.
    No preview · Article · Jan 2002
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    S. Dimitrova · I. Stoilova · T. Yanev

    Full-text · Article · Jan 2002
  • S. Dimitrova · I. Stoilova · T. Yanev
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    ABSTRACT: The influence of solar activity changes and related to them geomagnetic field variations on human health is confirmed in a lot of publications but the investigations in this area are still sporadic and incomplete because of the fact that it is difficult to separate the geomagnetic influence from the environmental factor complex, which influence the human life activity. That is why we have studied the influence of changes in geomagnetic activity on human physiological, psycho-physiological parameters and behavioural reactions. In this article we looked for influence of changes in GMA on the systolic and diastolic blood pressure and pulse-rate. We examined 54 volunteers. 26 persons of them had some cardio-vascular or blood pressure disturbances. The registrations were performed every day at one and the same time for each person during the period 1.10 - 10.11.2001. Four-way analysis of variance (MANOVA method) with factors: GMA, day, sex and cardiovascular pathology was performed. GMA was divided into four levels according to the Kp- and Ap-index values. The days examined were divided into six levels in relation to the day with increased GMA. Factor "cardiovascular pathology" was divided into two levels: healthy subjects and subjects that had some cardio -vascular or blood pressure disturbances. When we employed four-way analysis of variance, the influence of some of the factors on the physiological parameters examined turned out to be statistically significant at p<0.05. Our investigations indicate that most of the persons examined irrespectively to their status could be sensitive to the geomagnetic disturbances.
    No preview · Article · Jan 2002
  • T. K. Yanev · B. J. Choudhury · D. N. Mishev
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    ABSTRACT: More than one spectral class is usually found within a pixel when measuring the spectral reflectance characteristics (SRC) of natural formations in the visible (VIS) and near infrared (NIR) ranges of the electromagnetic spectrum. The spectral mixture "soil-vegetation" is a typical example. The decomposition of this mixture is strongly impeded because only the mixture SRC are usually available in result of a separate measurement, the soil SRC and the vegetation coverage coefficient p not being known in advance. This is especially true for remotely sensed data in field experiments where the soil SRC are only approximately known depending on the soil type. Nevertheless SRC of some soil types may be fitted satisfactory by linear functions of the wavelength. This fact reveals possibilities the linearly fitted soil SRC component to be eliminated irrespectively of the unknown parameters of the regression straight line in the concrete case of measurement. Under the assumption that the soil SRC are a linear function of the wavelength two SRC transforms were defined and studied in previous papers of the authors The first one named Soil-Free Coefficient (SFC) is a linear combination of three SRC of the mixture. It is free of the background soil contribution due to: - the proper choice of the wavelengths of the SRC included in SFC (the distance between adjacent wavelengths is constant); - under this condition the coefficients of the linear combination SFC are properly chosen, so that the soil SRC is eliminated; the vegetation coverage coefficient p participates as a multiplier of the rest part of the SFC expression. The second transform is thecoefficient, which is free of the unknown linear soil component as well as of the unknown coverage coefficient p. This is due to thestructure:is defined as a fraction of two SFC determined by means of two different triples of SRC. Therefore the p coefficient in the expression foris canceled. Socharacterizes only the canopy reflectance irrespective to the vegetation coverage coefficient In previous studies of the authorswas examined in the case when the soil SRC may be approximated by one straight line (SRC of chernozem and aluvial soils meet this requirement). In this workwas obtained and studied for soil types that may be satisfactory piece-wise approximated by two different crossing straight lines within the VIS and NIR ranges were studied. As it is known the vegetation coverage coefficient remains one and the same for all wavelengths. This allows the numerator to be calculated using one triple of SRC taken from the first straight line for example. Thedenominator may be calculated making use of a second triple of SRC within the second fitting straight line. As the vegetation coverage coefficient remains one and the same for all wavelengths and multiplies the expressions of the numerator and the denominator, it will be canceled. Thus thecoefficient may be employed to eliminate the unknown soil SRC from the measured mixture SRC in the case when the soil SRC are nonlinear wavelength function which may be fitted by two straight lines. Examples of USA and Bulgarian soil types are given in the study, which meet this requirement. SFC and thecoefficient may be used to remove an unknown linear background component from any other two - component spectral mixture as well. Thecoefficient does not depend on the coverage coefficient of the other component in addition. All results are easily generalized for a multi-component spectral mixture which contains a linear component.
    No preview · Article · Jan 2002
  • D. N. Mishev · T. K. Yanev
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    ABSTRACT: More than 8000 catalogued objects are now in geostationary orbits (GSO) and approximately 95% of them (inactive satellites, last rocket stages etc.) are not operating, i.e. they are in the list of space debris and their presence in GSO is not necessary. Therefore a significant risk exists any future launching not to be successful. In previous works of the authors the linear regression analysis was used to select those of the 323 geostationary objects in a drift orbit catalogued in the ESA's DISCOS Database, which are closely located around a straight line in the plane of two of their orbit parameters - the perigee and the apogee mean deviation from the geostationary orbit for example. Such type of clustering may contribute to reveal common technical and exploration conditions which have caused deviations in their orbit parameters. In this work the same set of objects as well as updated data referred to year 2001 were examined, making use of a transform known as the contrast coefficient-ND (normalized difference) and named herein the apogee-perigee contrast coefficient (APCC). It was shown that the usage of APCC may reveal new clusters in comparison with the linear regression line.
    No preview · Article · Jan 2001
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    I Stoilova · T Zdravev · T Yanev

    Preview · Article · Feb 2000 · Doklady Bolgarskoi akademii nauk
  • I Stoilova · T Zdravev · T Yanev · S Zdraveva

    No preview · Article · Feb 2000 · Aviakosmicheskaia i ekologicheskaia meditsina = Aerospace and environmental medicine