A. K. Shukla1, Y. P. Desai1, A. Garg1, P. R. Nair2, V. R. Bhavsar1 and S. S. Palsule1
1Data Quality Evaluation Division, Signal Image and Information Processing Area, Space Applications Centre, Ahmedabad – 380 053
2Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthpuram – 695 022
With large number of space borne sensors being launched in space by ISRO and other space agencies such as NASA, ESA, NASDA etc., it has become necessary and essential to establish a relationship between the data obtained by different sensors so that data of one sensor could be translated to other sensor data in terms of standard radiometric units for better quantitative and meaningful utilization of remote sensing data for the study of Earth resources. In order to calibrate the sensor, it is essential to know the atmospheric conditions at the time of data acquisition over the known reference site so that data normalization could be carried out by computing the atmospheric transmittance, path radiance and total downwelling irradiance incident on the calibration site. Further, it is also necessary to know the background reflectance of the area in which calibration site is located. This paper discusses an in-flight vicarious calibration technique developed at Space Applications Centre, Ahmedabad for absolute radiance calibration of space borne remote sensing sensors in orbit. The technique is very useful to the study sensor performance degradation over its useful mission life and also to update radiometric calibration coefficients used in the generation of standard data products. The three major components of the technique are:
- design / development of an accurate correction procedure using radiative transfer approach and spectral optical inversion techniques
- design / development of an artificial calibration site ‘CHHARODI’ near Ahmedabad for moderate and high spatial resolution multi-spectral sensors using five different reflectivity targets covering full dynamic range of sensors
- use of ground based accurately calibrated Spectro-radiometer and Sun photometer/ Ozonometer for the measurement of artificial target radiance/reflectance, atmospheric spectral optical depths, olar irradiance etc. at the time of satellite pass
Results of recent experiment, conducted on this site when IRS-1C and IRS-1D passes were observed on the same day, is reported in this paper. An operational scheme drawn to inter-calibrate sensor data of IRS-1C and 1D, IRS-P6, CARTOSAT-1 and 2, IKONOS, LANDSAT-7, SPOT-4 etc. using artificial targets at CHHARODI calibration site and future plans are described in the paper.