However, the GSICS community faces several challenges. The first being that while, the inter-comparing global means is able to empirically correct mean biases in the monitored instrument during its active operation, this assumption is not adequate to re-calibrate the monitored instrument permanently correct any biases over the life of the sensor. For a re-calibration, one needs to know the cause of the biases; thus, it is important to select a reference instrument with minimal scan angle dependence, minimal temperature dependence bias and which is extremely stable so that its inter-comparison with the monitored instrument is able to reveal these biases in the monitored instrument. The second challenge is to identify suitable in-orbit reference for monitoring for microwave sensors. It is widely recognized that microwave instruments have not demonstrated stability that is comparable to IR instruments so as to directly act as references.
The first goal of this presentation is to define a GSICS reference selection criterion (Weng 2016, Bali 2016) that uses stringent (evaluates scan angle, spectral, temperature time dependent biases) conditions to select reference instruments. We apply this on selection of IR and microwave instruments and show that IASI -A, AIRS and CrIS fulfill our selection criterion. Our second goal is to propose the use of Fundamental Climate Data Record (FCDR, Zou 2016 ) as an in-orbit reference for microwave instruments. We will show that the FCDR fulfills the selection criterion and can act as a robust reference for monitoring the S-NPP ATMS sensor. We would also suggest a path forward to mitigate the impact of anomalies in reference instrument on inter-comparison results and suggest the use ‘reference records’ (Flynn and Bali, 2016) instead of using directly level 1 radiances.
Bali, M.(2016): Comparisons of IASI-A and AATSR measurements of top-of-atmosphere radiance over an extended period. , Atmos. Meas. Tech. Discuss., 8, 9785-9821, doi:10.5194/amtd-8-9785-2015
Bali et al ( 2016): Selecting a GSICS reference instrument IR , VIS and Microwave: GSICS- Annual Meeting, Tokyo: http://gsicswiki.net/pub/Development/20160229/3e_manik_reference.pptx
Zou C-Z (2013) Atmospheric temperature climate data records from satellite microwave sounders.Source: Satellite-based Applications on Climate Change Pages: 107-125 Published: 2013/01/01 DOI: 10.1007/978-94-007-5872-8_8
Weng , (2016): CEOS/WGCV :http://ceos-gsics.csp.escience.cn/dct/page/1