Active-Passive Algorithm for Nisar High Resolution Soil Moisture Products Over India

This study demonstrate the suitability of an Active-Passive algorithm for the upcoming NASA-ISRO SAR (NISAR) mission to generate high resolution (at sub-km) soil moisture products over India. This algorithm utilize the high resolution ($\sim 25 \mathrm{~m}$) SAR data from ISRO’s EOS-04 C-band SAR mission and coarse ($\sim 9 \mathrm{~km}$) L-band brightness temperature from NASA’s SMAP to generate high resolution ($\sim 500 \mathrm{~m}$) soil moisture product over Indian regions for agricultural applications, especially for irrigation scheduling, crop water demand and crop stress management etc. In this work, we adopted and modified the Active-Passive (snapshot approach) soil moisture algorithm to evaluate its effectiveness at sub-kilometer scale ($\sim 500 \mathrm{~m}$). The high resolution soil moisture ($\sim 500 \mathrm{~m}$) have been validated over multiple dates, covering Kharif and Rabi seasons with multiple crop conditions over selected site. A good agreement was observed with in-situ datasets with ubRMSE, ranging from 0.039 to $0.06 \mathrm{~m} 3 / \mathrm{m} 3$ as an accuracy metric which demonstrated the potential of an Active-Passive algorithm for soil moisture retrieval using NISAR data at sub-km grid with required accuracy, in order to meet the agricultural application requirements.