• N R Patel

      Articles written in Journal of Earth System Science

    • Assessing the consistency between AVHRR and MODIS NDVI datasets for estimating terrestrial net primary productivity over India

      R K Nayak N Mishra V K Dadhwal N R Patel M Salim K H Rao C B S Dutt

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      This study examines the consistency between the AVHRR and MODIS normalized difference vegetation index (NDVI) datasets in estimating net primary productivity (NPP) and net ecosystem productivity (NEP) over India during 2001–2006 in a terrestrial ecosystem model. Harmonic analysis is employed to estimate seasonal components of the time series. The stationary components (representing long-termmean) of the respective NDVI time series are highly coherent and exhibit inherent natural vegetation characteristics with high values over the forest, moderate over the cropland, and small over the grassland. Both data exhibit strong semi-annual oscillations over the cropland dominated Indo-Gangetic plains while annual oscillations are strong over most parts of the country. MODIS has larger annual amplitude than that of the AVHRR. The similar variability exists on the estimates of NPP and NEP across India. In an annual scale, MODIS-based NPP budget is 1.78 PgC, which is 27% higher than the AVHRR-based estimate. It revealed that the Indian terrestrial ecosystem remained the sink of atmospheric CO$_2$during the study period with 42 TgC y$^{−1}$ NEP budget associated with MODIS-based estimate against 18 TgC y$^{−1}$ for the AVHRR-based estimate.

    • Assessment of large aperture scintillometry for large-area surface energy fluxes over an irrigated cropland in north India

      Abhishek Danodia V K Sehgal N R Patel R Dhakar J Mukherjee S K Saha A Senthil Kumar

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      Amount of available net energy and its partitioning into sensible, latent and soil heat fluxes over an agricultural landscape are critical to improve estimation of evapotranspiration and modelling parse (ecosystem modelling, hydrological and meteorological modelling). Scintillometry is a peculiar and robust methodology to provide structure parameter of refractive index and energy balance. Scintillometer has proven for assessment of sensible and latent heat flux, which is based on the principle of Monin–Obukhov similarity theory. Scintillometer has been installed in the agricultural experimental farm of ICAR-Indian Agricultural Research Institute, New Delhi, with a spatial covering path length of 990 m of irrigated and cultivable agricultural landscape. This paper discusses the patterns of energy flux as diurnal and seasonal basis at scintillometer path which was mainly covered by maize in Kharif and wheat in Rabi season during a crop growing seasons of 2014–2015. The biophysical parameters (leaf area, soil moisture, crop height) were recorded at a temporal resolution of fortnight basis along the path length at usual sampling distance. The Bowen ratio value for both Kharif and Rabi season was 0.76 and 0.88, respectively by scintillometer. Leaf area index had a significantly positive correlation with latent heat flux ($R^{2} =0.80$) while a significantly negative correlation with sensible heat flux ($R^{2}{=}-0.79$). Soil moisture had a significant negative correlation with sensible heat flux ($R^{2}{=}-0.68$). The average evapotranspiration from crop land was 1.58 mm d−1 and total evapotranspiration was 543 mm over the 12 months study period. This study defines that large aperture scintillometer is robust instrument which can evaluate energy flux over a large area with a long term series time domain. Moreover, further studied should be conducted to use in crop simulation modelling, developing of new model with calibration and validation of remote sensing energy balance algorithm, etc.

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