Testing the VIIRS operational code with a proxy data stream

In preparation for the launch of the NPOESS Preparatory Project (NPP) satellite in 2011, the science code needed to create environmental data records (EDRs) from data collected by each sensor on board (i.e., VIIRS, CrIS, ATMS and OMPS) has been operationalized and hosted in the Interface Data Processing Segment. To test the prelaunch functionality and performance of these operational algorithms, a proxy data stream was generated for each of these NPP sensors. For the VIIRS sensor, twelve orbits of MODIS Aqua data from two separate golden days were processed into 6, two-orbit VIIRS proxy datasets. There were four major steps required to generate the proxy data. The first step was to spatially and spectrally remap MODIS L1B radiances to emulate what would be observed by the VIIRS sensor on an NPP orbit. This involved generating NPP ephemeris and attitude data, performing VIIRS pixel geolocation and then spatially and spectrally remapping the MODIS L1B radiances to the nearest VIIRS pixels. The second step was to fill in data missing from the remapped VIIRS swath with realistic values. There are three main reasons for this missing data: The MODIS swath on the EOS-Aqua orbit is narrower than the VIIRS swath on NPP, MODIS ocean bands saturate at lower radiance values than the corresponding dual gain VIIRS bands, and MODIS Aqua has dead detectors for some bands. The third step was to use a detailed model of the VIIRS sensor to create level 0 data, verified Raw Data Records (RDR) in VIIRS terminology, including VIIRS instrument artifacts. The final step was to package the data into the raw data format output by the VIIRS instrument. To test functionality and performance, the raw sensor and spacecraft data were processed by the operational code. A subset of this data was also run from the verified RDR level to produce EDRs using the science code baseline for comparisons. Details of the steps outlined above will be presented as well as testing procedures and results.