NPP VIIRS Early On-Orbit Geometric Performance

The NASA/NOAA Visible Infrared Imager Radiometer Suite (VIIRS) instrument on-board the Suomi National Polar-orbiting Partnership satellite was launched in October 2011. Assessment of VIIRS' geometric performance includes measurements of the sensor's spatial response, band-to-band co-registration (BBR), and geolocation accuracy and precision. The instrument sensor (detector) spatial response is estimated by line spread functions (LSFs) in the scan and track directions. The LSFs are parameterized by dynamic field of view in the scan direction and instantaneous FOV in the track direction, modulation transfer function for the 16 moderate resolution bands (M-bands), and horizontal spatial resolution for the five imagery bands (I-bands). VIIRS BBR for the M and I bands is defined as the overlapped fractional area of angular pixel sizes from the corresponding detectors in a band pair, including nested I-bands into M-bands, and measured on-orbit using lunar and earth data. VIIRS geolocation accuracy and precision are affected by instrument parameters, ancillary data (i.e., ephemeris and attitude), and thermally induced pointing variations with respect to orbital position. These are being tracked by a ground control point matching program and corrected in geolocation parameter lookup tables in the ground data processing software. This on-orbit geometric performance assessment is an important aspect of the VIIRS sensor data record calibration and validation process. In this paper, we will discuss VIIRS' geometric performance based on the first seven-month of VIIRS' on-orbit earth and lunar data, and compare these results with the at-launch performance based on ground test data and numerical modeling results. Overall, VIIRS' on-orbit geometric performance is very good and matches the prelaunch performance, and is thus expected to meet the needs of both the long-term monitoring and operational communities.