BENGALURU: The multiple levels of data have been successfully generated by the Global Navigation Satellite System- Reflectometry (GNSS-R) instrument on the EOS-08 satellite, scientists and researchers from Indian Space Research Organisation (ISRO) said on Wednesday.
The raw data is being processed at the National Remote Sensing Centre (NRSC-ISRO) in Shadnagar, Hyderabad, using algorithms and data processing software developed by the Space Applications Centre (SAC-ISRO), Ahmedabad.
The GNSS-R represents a new mode of remote sensing. Signals from Global and Regional Navigation Satellite Systems, such as GPS and NavIC, are reflected off various earth surfaces, including oceans, farm lands and river bodies. These reflected signals are collected by a precision receiver onboard the satellite as it orbits the Earth at an altitude of 475 km. This system operates without dedicated transmitters and is shallow in resource consumption — requiring minimal size, weight and power. It can also scale up as a constellation of receivers for faster coverage, making this innovative remote-sensing mode highly useful, the release said.
The GNSS-R instrument, developed by the Space Applications Centre (SAC-ISRO), is India’s first space-borne precision receiver. It collects ground- reflected GNSS signals and measures their power and other signal characteristics. These measurements are used to derive scientific information about the regions covered by the receiver, including soil moisture, surface inundation and ocean surface wind and wave measurements.
Delay- Doppler Maps (DDMs) are primary outputs from GNSS-R raw data processing. These DDMs are used to derive parameters such as reflectivity and Normalized Bistatic Radar Cross- Section (NBRCS), which are then used for the retrieval of various scientific parameters. While calibration and validation are ongoing, these results demonstrate the immense potential of this instrument for various scientific studies and applications, the release added.
All the science products are generated at SAC-ISRO using in-house developed algorithms. The first land data was collected over the Sahara Desert (North Africa) using a high-resolution mode of 1 km, which is significantly better than that of contemporary CYGNSS sensors. This data was processed to retrieve soil moisture at high resolution, and the results were found to be within the expected range. Another high-resolution land dataset was acquired over the Amazon Rainforest on August 21.
This data has been used to generate surface inundation masks along the specular reflection track, showing sensitivity even towards sub-kilometre river widths. The first ocean data was collected on August 19, over a region of the Pacific Ocean. This data was processed for the retrieval of wind speed and significant wave height, with all obtained values falling within the expected ranges.