Abstract
Abstract. Vicarious calibration refers to methods that make use of “invariant” natural targets of the Earth for the post-launch calibration of sensors. This process of calibration is useful for initial phase orbit operation of sensor and thereafter for validation during its operational span. This method of periodic evaluation of radiometric and geometric performance of the space-borne optical sensors and validation of derived radiance/reflectance is to ensure availability of consistent and accurate data products to the user community. This paper describes one such Cal/Val facility’s design, engineering aspects and realization at National Remote Sensing Centre (NRSC), Shadnagar. The target materials used for filling the Cal/Val site are studied for its reflectance. These targets have reflectance ranging from 9% to 53%, in the VNIR (Visible and Near Infra-Red) region. This paper also describes instruments used for calibration and homogeneity studies of targets for its invariance since operationalisation (January 2016). The last section of this paper is about reflectance based absolute radiometric calibration of medium resolution Indian Remote Sensing (IRS) sensor (Resourcesat and Cartosat series) using RT model and edge based LSF/MTF estimation of high resolution sensor carried out using the Cal/Val facility.
Highlights
Periodic evaluation of radiometric and geometric performance of the space-borne optical sensors and validation of satellite derived radiance/reflectance of earth scenes using these sensors are becoming mandatory requirements to ensure availability of consistent and accurate data products to the user community
Natural sites internationally identified for Cal/Val activities are mostly based on uniform deserts, dry lake beds/playas, large salt pans and snow features that are scattered across globe
Due to the limitation of clear sky conditions and monsoon season, the favourable period for experiments is between October to April only
Summary
Periodic evaluation of radiometric and geometric performance of the space-borne optical sensors and validation of satellite derived radiance/reflectance of earth scenes using these sensors are becoming mandatory requirements to ensure availability of consistent and accurate data products to the user community. The need for inter-operability of sensors to fill data gaps over different regions using data from multiple sensors calls for inter-sensor comparison between different space-borne sensors. It calls for using a unified scale of measurement bringing in traceability. Satellite sensors with spatial resolutions of 30m or better can be characterised with the targets (i.e soils & stones) available in larger area. Sensors of sub-metre spatial resolution can be characterised on the uniquely designed structure (Raghu Venkataraman et al, 2015) with paint targets.
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