H. J. Trivedi

N.V. Patel College of Pure and Applied Sciences, Aimand, Gujarāt, India

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Publications (8)7.22 Total impact

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    ABSTRACT: Indian geostationary satellite Kalpana-1 (K1) offers a potential to capture the diurnal cycle of land surface temperature (LST) through thermal infrared channel (10.5–12.5 μm) observations of the Very High Resolution Radiometer (VHRR) sensor. A study was carried out to retrieve LST by adapting a generalized single-channel (SC) algorithm (Jiménez-Muñoz and Sobrino, 2003) for the VHRR sensor over India. The basis of SC algorithm depends on the concept of Atmospheric Functions (AFs) that are dependent on transmissivity, upwelling and downwelling radiances of the atmosphere. In the present study AFs were computed for the VHRR sensor through the MODTRAN simulations based upon varying atmospheric and surface inputs. The AFs were fitted with the atmospheric columnar water vapour content and a set of coefficients was derived for LST retrieval. The K1-LST derived with the SC algorithm was validated with (a) in situ measurements at two sites located in western parts of India and (b) the MODIS LST products. Comparison of K1-LST with the in situ measurements demonstrated that SC algorithm was successful in capturing the prominent diurnal variations of 283–332 K in the LST at desert and agriculture experimental sites with a rmse of 1.6 K and 2.7 K, respectively. Inter comparison of K1-LST and MODIS LST showed a reasonable agreement between these two retrievals up to LST of 300 K, however a cold bias up to 7.9 K was observed in MODIS LST for higher LST values (310–330 K) over the hot desert region.
    ISPRS Journal of Photogrammetry and Remote Sensing 01/2014; 94:160–168. · 3.31 Impact Factor
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    ABSTRACT: Spectral features of plant species in the visible to SWIR (0.4–2.5 μm) region have been studied extensively, but scanty attention has been given to plant thermal infrared (TIR: 4–14 μm) properties. This paper presents preliminary results of a study that was conducted first time in India to measure radiance and emissivity properties of eight plant species in TIR spectral region in the field conditions using a FTIR (Fourier Transform Infrared) field spectroradiometer working in 4–14 μm at an agriculture experimental farm. Several spectral features in the emissivity spectra of plant species were observed that are probably related to the leaf chemical constituents, such as cellulose and xylan (hemicellulose) and structural aspects of leaf surface like abundance of trichomes and texture. Observations and results from the field measurements were supported by the laboratory measurements like biochemical analysis. These preliminary field emissivity measurements of leaves in TIR show that there is useful spectral information that may be detectable by field-based instrument. More detailed field and laboratory measurements are underway to explore this research theme.
    Journal of the Indian Society of Remote Sensing 12/2013; · 0.53 Impact Factor
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    D Shah, M Pandya, H Trivedi, A Jani
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    ABSTRACT: Spatially distributed air temperature data are required for climatological, hydrological and environmental studies. However, high spatial distribution patterns of air temperature are not available from meteorological stations due to its sparse network. The objective of this study was to estimate high spatial resolution minimum air temperature (T min) and maximum air temperature (T max) over the Indo-Gangetic Plain using Moderate Resolution Imaging Spectroradiometer (MODIS) data and India Meteorological Department (IMD) ground station data. T min was estimated by establishing an empirical relationship between IMD T min and night-time MODIS Land Surface Temperature (T s). While, T max was estimated using the Temperature-Vegetation Index (TVX) approach. The TVX approach is based on the linear relationship between T s and Normalized Difference Vegetation Index (NDVI) data where T max is estimated by extrapolating the NDVI-T s regression line to maximum value of NDVImax for effective full vegetation cover. The present study also proposed a methodology to estimate NDVImax using IMD measured T max for the Indo-Gangetic Plain. Comparison of MODIS estimated T min with IMD measured T min showed mean absolute error (MAE) of 1.73°C and a root mean square error (RMSE) of 2.2°C. Analysis in the study for T max estimation showed that calibrated NDVImax performed well, with the MAE of 1.79°C and RMSE of 2.16°C.
    Journal of Earth System Science 01/2013; 122(6). · 0.70 Impact Factor
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    D B Shah, M R Pandya, H J Trivedi, A R Jani
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    ABSTRACT: Minimum and maximum air temperatures (hereafter called Ta min and Ta max) are important climatological variables and accurate mapping its spatial-temporal distribution is useful in wide range of applications in the field of ecology, hydrology and atmospheric sciences. Air temperature (Ta) has been traditionally measured at large number of meteorological stations. However such meteorological measurements are not usually available with enough spatial density for accurate research purposes (Vogt et al., 1997; Willmott et al., 1991). The spatio-temporal pattern of near surface Ta is complex because it is affected by properties that vary greatly in both space and time (Prihodko and Goward, 1997). Satellite-based remote sensing technique is an alternative to provide spatially distributed information, because of its capability of systematic and synoptic coverage over a large geographical area (Czajkowski et al., 1997; Goward et al., 1994). The satellite-derived Land Surface Temperature (Ts) has a significant relationship with the Ta in the ABSTRACT Minimum and maximum air temperatures are important input parameters for meteorological and agricultural models. Generally minimum and maximum air temperatures are measured at weather stations on the ground. However these measurements are not available with enough spatial density which makes it difficult to be used in real-time applications. Compensation of this lack of information can be achieved by satellite-based methods. The present study investigates the potential of deriving the spatial distribution of minimum and maximum air temperatures with the help of land surface temperature (Ts) and normalized differential vegetation index (NDVI) products from the moderate resolution imaging spectroradiometer (MODIS) sensor and air temperature (Ta) data from automatic weather stations (AW S) over Gujarat region of India. The minimum Ta was successfully retrieved through a regression analysis between nig ht time MODIS Ts and AW S measured minimum Ta over all stations, since the minimum Ta is strongly associated with night time Ts. W hile, the maximum Ta was retrieved using a method, namely, temperatu re vegetation index (TVX) approach based on the linear relationship between Ts and NDVI data. Results showed that MODIS estimated minimum Ta were in good agreement with the measured values by mean absolute error (MAE) of 1.49 0 C and root mean square error (RMSE) of 1.95
    Journal of agrometeorology 12/2012; 14(14):111-118. · 0.15 Impact Factor
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    ABSTRACT: INSAT-3D is the new generation Indian Earth observation satellite to be launched by ISRO in near future. It will provide enhanced observations of land, ocean and atmosphere through two payloads namely Imager and Sounder from geostationary orbit. The Imager payload is designed to sense solar-reflected and radiant energy from the Earth through six channels covering visible (VIS: 0.55-0.75µ m), shortwave infrared (SWIR: 1.551.70µm), middle infrared (MIR: 3.8-4.0µm), water vapor infrared (WVIR: 6.5-7.1µm) and thermal infrared (TIR1: 10.3-11.3µm and TIR2: 11.5-12.5µm) spectral regions. The TIR1 and TIR2 are two thermal channels that can be used to derive a key geophysical parameter- land surface temperature (LST) through a split-window algorithm. To derive LST from various satellite-based sensors several types of split-window (SW) algorithms have been developed in the past 25 years; however, SW algorithm for Indian sensor has not been attempted. A study has been conducted with the objective to identify the most suitable SW algorithm for LST retrieval from the INSAT-3D Imager thermal infrared observations. A systematic exercise was carried out involving evaluation and comparison of 10 published SW algorithms. The evaluation of algorithms was done through two major steps: (a) Simulation of at-sensor thermal signal by a radiative transfer model- MODTRAN (MODerate spectral resolution atmospheric TRANSmittance) and (b) Derivation of split-window coefficients (SWC) of 10 algorithms of LST retrieval. The simulations were carried out in the split thermal channels by varying following input parameters: temperature of the atmospheric lower boundary through atmospheric profiles, atmospheric columnar water vapour, surface temperature, view zenith angle and land surface emissivity over 10 different land cover types. Once the simulation process was over, the SWC were generated for 10 LST algorithms. The results were inter-compared by computing the total error in the estimation of LST by classical error theory. Based upon the inter comparison analysis, we found that Sobrino et al. (1996) performed superior with coefficient of determination (R) of more than 0.96 and the RMSE of around 1.43 K therefore it is selected for further analysis.
    12/2011: pages 35-41; , ISBN: 0970-1397
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    ABSTRACT: INSAT-3D is the new generation Indian satellite designed for improved Earth observations through two payloads – Imager and Sounder. Study was conducted with an aim of simulating satellite level signal over land in the infrared channels of the Imager payload using a radiative transfer model MODTRAN. Satellite level at-sensor radiance corresponding to all four infrared channels of INSAT-3D Imager payload is obtained using MODTRAN and sensitivity of at-sensor radiance was inferred as a function of input parameters namely, surface temperature, emissivity, view angle and atmospheric water vapour, which is helpful in understanding the signal simulation scheme needed for retrieving a very critical parameter namely, land surface temperature. Keywords.Earth observation; imager; INSAT-3D; land surface; MODTRAN; simulation; thermal infrared.
    Journal of Earth System Science 01/2011; 120(1):19-25. · 0.70 Impact Factor
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    ABSTRACT: Recently proposed model potential for describing the electron–ion interaction is employed to calculate total energy, energy band gap at Jones-zone face at X, equation of state and bulk modulus of GaP, GaAs and GaSb compounds using higher-order perturbation theory. The covalent correction term corresponding to third- and fourth-order perturbation energy terms are used to take account of covalent bonding effect in such semiconductors. The significant value of the covalent bonding term shows the essentiality of higher-order correction for zincblende-type crystals. We have employed five different screening functions alongwith the latest screening function proposed by Sarkar et al. in the present work. The numerical results for the total energy, energy band gap at Jones-zone face and bulk modulus of these compounds are in good agreement with the experimental data and found better than other such theoretical findings. The pressure and bulk modulus at different volumes are obtained by using such higher-order perturbation theory with the application of our model potential. The pressure obtained by this method is compared with pressure obtained by equations proposed by Murnarghan and Vinet et al. The present study also shows that the incorporation of different screening functions generates distinct effects.
    Physica B Condensed Matter 01/2005; 357(3):305-311. · 1.28 Impact Factor
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    ABSTRACT: Recently proposed model potential which combines both linear and quadratic types of interactions is employed for the investigation of some properties like the total energy, equation of state and bulk modulus of AlP, AlAs and AlSb semiconductor compounds using higher-order perturbation theory. The model potential parameter is determined using zero pressure condition. The ratio of the covalent bonding termE cov to the secondorder termE 2 is 6.77% to 11.85% which shows that contribution from higher order terms are important for zinc-blende-type crystals. The calculated numerical results of the total energy, energy band gap at Jones-zone face and bulk modulus of these compounds are in good agreement with the experimental data and found much better than other such theoretical findings. We have also studied pressure-volume relations of these compounds. The present study is carried out using six different screening functions along with latest screening function proposed by Sarkaret al. It is found from the present study that effect of exchange and correlation is clearly distinguishable.
    Pramana 64(1):153-158. · 0.56 Impact Factor