Comparison of VIIRS pre-launch RVS performance using results from independent studies

Abstract

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor carried on the NPOESS (National Polar-orbiting Operational Environmental Satellite System) Preparatory Project (NPP) mission [1] (http://jointmission.gsfc.nasa.gov/viirs.html), and is scheduled to launch in October 2011. VIIRS sensor design draws on heritage instruments including AVHRR, OLS, MODIS, and SeaWiFS. It has on-board calibration components including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view (SV) port for background subtraction. These on-board calibrators are located at fixed scan angles. The VIIRS response versus scan angle (RVS) was characterized prelaunch in lab ambient conditions and will be used on-orbit to characterize the response for all scan angles relative to the calibrator scan angle (SD for RSB and blackbody for TEB). Since the RVS is vitally important to the quality of calibrated radiance products, several independent studies were performed and their results were compared and validated. This document provides RVS results from three groups: the NPP Instrument Calibration Support Team (NICST), Raytheon, and the Aerospace Corporation. A comparison of the RVS results obtained using a 2 nd order polynomial fit to measurement data is conducted for each band, detector, and half angle mirror (HAM) side. The associated RVS fitting residuals are examined and compared with the relative differences in RVS found between independent studies. Results show that the agreement is within 0.1% and comparable with fitting residuals for all bands except for RSB band M9, where a difference of 0.2% was observed. Band M9 is highly sensitive to the atmospheric water vapor variations during the sensor ambient testing at Raytheon, and its correction Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx might be a contributor to the observed RVS uncertainty differences. In general, NICST results have shown slightly larger RSB RVS uncertainties but still well within the 0.3% total uncertainty allowed for the RVS characterization defined in the Performance Verification Plan.

SNPP VIIRS thermal emissive band thermal calibration errors and their impact on radiance and brightness temperature retrieval

“…However the view geometry differences between SV, EV and OBCBB sectors require inclusion of a response versus scan angle (RVS) component to account for Half Angle Mirror (HAM) reflectance differences between them [2]. Residual instrument thermal background emission due to RVS difference between paths comes from the rotating telescope assembly (RTA), which precedes the HAM in the optical path and from the HAM itself.…”

VIIRS reflective solar bands on-orbit calibration coefficient performance using imagery and moderate band intercomparisons

“…The view geometry differences on the HAM, a response versus scan angle (RVS) component is needed to account for HAM reflectance differences between the two paths RVS EV and RVS SD [4]. The RVS is a relative reflectance variation over VIIRS scan angles and is normalized to 1 at the SV angle of -65.5º.…”

Initial on-orbit radiometric calibration of the Suomi NPP VIIRS reflective solar bands

“…RVS (Response Versus Scan) is the reflectivity of the Half-Angle-Mirror (HAM) of VIIRS, an incident angle dependent quantity 4 . The HAM is an integral part of the sensor, residing right after the Rotating Telescope Assembly (RTA) in the optical path.…”