End-to-end performance assessment of the National Polar-orbiting Operational Environmental Satellite System environmental data records

Abstract

The tri-agency Integrated Program Office (IPO) is managing the development of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). Later this decade, the IPO, through its prime contractor, Northrop Grumman Space Technology (NGST), will launch NPOESS spacecraft into three orbital planes (1330, 1730, and 2130 equatorial ascending nodal crossing times) to provide global coverage with a data refresh rate of approximately four hours. A globally distributed ground system will deliver 95 percent of the data within 26 minutes from the time of on-orbit collection. With the development of NPOESS, we are evolving the existing "weather" satellites into integrated environmental observing systems. To meet user-validated requirements, NPOESS will deliver global data for 55 Environmental Data Records (EDRs). Performance characteristics and attributes have been defined for each of the 55 parameters, including: horizontal/vertical resolution; mapping accuracy; measurement range; measurement precision and uncertainty; refresh rate; data latency; and geographic coverage. Long-term stability requirements have been defined for key parameters to ensure temporal consistency and continuity of data over the operational life of NPOESS. The actual EDR performances will be a result of the sensor and algorithm performances. In order for NPOESS program to determine estimates of EDR performance based on current design data and to assess potential sensor design changes or algorithm modifications, NGST developed an Integrated Weather Products Test Bed (IWPTB). This system can generate simulated radiances from mission/orbit variable, sensor variables, atmospheric and background conditions, and radiative transfer models. These simulated radiances at aperture are used with sensor models and spacecraft factors to generate simulated radiometric temperatures which are processed by science retrieval code to generate EDRs. This paper presents an assessment of the impact of the VIIRS sensor design modification to correct Modulated Instrument Background in the sensor's optical train. This assessment, which focuses on the Sea Surface Temperature EDR in particular, was generated by the IWPTB end-to-end performance assessment capability.

Comparison of the University of California at Los Angeles Line-by-Line Equivalent Radiative Transfer Model and the Moderate-Resolution Transmission Model for accuracy assessment of the National Polar-Orbiting Operational Environmental Satellite System’s Visible–Infrared Imager–Radiometer Suite cloud algorithms

“…Multiple scattering within clouds is simulated by the DISORT. Although a larger number (as many as 256) of streams is required for satisfactory computational accuracy, it is estimated that, for an extensive simulation effort such as the generation of global test data sets, 22 the optimal number of streams for speedy yet reasonably accurate calculation of reflectances and radiances is 16. 5 Initially, we acquired only M1, into which the phase function is invariably built as the H-G phase function for both ice and water clouds and for all wavelengths.…”

“…We estimate that retrievals that use MODTRAN4 simulated reflectances and VIIRS lookup tables (from the LBLE) will produce errors that are close to NPOESS EDR threshold requirements. 22 Figures 3 and 5 also show comparisons of CPU time. For all spectral bands and for both ice and water cloud, the LBLE is at least ten times faster than the MODTRAN in the computation of nadir reflectance.…”