|Title||Response versus scan-angle corrections for MODIS reflective solar bands using deep convective clouds |
|Publication Type||Presentation |
|Year of Publication||2016 |
|Authors||Bhatt, R., A. Angal, D. R. Doelling, X. Xiong, A. Wu, C. O. Haney, B. Scarino, and A. Gopalan |
|Proceedings||Proc. of SPIE Earth Observing Missions and Sensors: Development, Implementation, and Characterization IV |
|MCST Conference||Proc. of SPIE Earth Observing Missions and Sensors: Development, Implementation, and Characterization IV |
The absolute radiometric calibration of the reflective solar bands (RSBs) of Aqua- and Terra-MODIS is performed using
on-board calibrators. A solar diffuser (SD) panel along with a solar diffuser stability monitor (SDSM) system, which
tracks the degradation of the SD over time, provides the baseline for calibrating the MODIS sensors. MODIS also views
the moon and deep space through its space view (SV) port for lunar-based calibration and computing the background,
respectively. The MODIS instrument views the Earth’s surface using a two-sided scan mirror, whose reflectance is a
function of the angle of incidence (AOI) and is described by response versus scan-angle (RVS). The RVS for both
MODIS instruments was characterized prior to launch. MODIS also views the SD and the moon at two different AOIs.
There is sufficient evidence that the RVS is changing on orbit over time and as a function of wavelength. The SD and
lunar observation scans can only track the RVS variation at two AOIs. Consequently, the MODIS Characterization
Support Team (MCST) developed enhanced approaches that supplement the onboard calibrator measurements with
responses from the pseudo-invariant desert sites. This approach has been implemented in Level 1B (L1B) Collection 6
(C6) for select short-wavelength bands. This paper presents an alternative approach of characterizing the mirror RVS to
derive the time-dependent RVS correction factors for MODIS RSBs using tropical deep convective cloud (DCC) targets.
An initial assessment of the DCC response from Aqua-MODIS band 1 C6 data indicates evidence of RVS artifacts,
which are not uniform across the scans and are more prevalent at the beginning of the earth-view scan.