Ensuring Continuity in the Earth Radiation Budget Climate Data Record: Radiation Budget Instrument
CERES sensors are currently flying on NASA's Terra and Aqua spacecraft (launched in December 1999 and May 2002) and on the Suomi-NPP spacecraft (launched in October 2011). The final CERES instrument, Flight Model 6, will fly on JPSS-1 in 2016.
To minimize discontinuities in the CDR, RBI will be required to make measurements which can be processed by the CERES Data Processing System with minimal modifications. The same data products will be generated for RBI as for CERES.
The reflected solar radiance and Earth-emitted radiance measurements will be used to compute fluxes for each pixel. Data from VISSR (Visible and Infrared Imaging Spectroradiometer), also on the JPSS spacecraft, are used to identify cloud properties for selection of bidirectional reflectance models to retrieve fluxes from radiances.
To ensure continuity with the CERES data products, RBI is presently being designed as a scanning radiometer to measure solar radiation reflected by the Earth and the outgoing longwave radiation to one percent and half percent accuracy, consistent with the current CERES sensors. RBI will fly aboard JPSS spacecraft beginning with JPSS-3, to be ready for launch in 2021.
RBI will have three channels: a shortwave, a longwave and a total channel. The shortwave channel will measure sunlight reflected by Earth, which is between 0.2 and 5 microns. The longwave channel will measure radiation emitted by the Earth, i.e. in the range 5 to 50 microns. The total channel will measure the full range from 0.2 to 100 microns, to directly measure the total amount of thermal energy leaving the earth-atmosphere system.
The field of view FOV of RBI will be a hexagon that is 2.6 degrees across the corners and 1.3 degrees across the sides, as was the FOV for CERES. The pixel size at nadir will be ~28 km. The point response function of RBI will be very similar to that of CERES, which was optimized by the condition that spatial sampling errors be minimized. This will make the data very similar to that of CERES.
RBI must be capable of operating in the scan modes which are used for the calibration techniques and validation protocols established by CERES to obtain the required accuracy. The standard scan mode is cross-track scanning to map the radiation field over the swath of Earth visible from the spacecraft. The scan mode can be programmed in flight to accomplish a number of tasks, including lunar observations for calibrations and validation of pointing accuracy, co-alignment with measurements from instruments on other spacecraft and multiple views of selected Earth scenes during an overpass.
RBI is funded by NASA's Science Mission Directorate. Langley Research Center's Flight Projects Directorate has responsibility for project management during the sensor acquisition phase and the Science Directorate has the responsibility for science operations and data product generation. Exelis was selected as the vendor for design, construction and testing of RBI. Ground calibration will be performed by Space Dynamics Laboratory of Utah State University under a contract from Exelis.
After successful completion of an Operational Handoff Review (approximately 90-days after launch), the CERES Science Team will have responsibility for operation of RBI and the processing of the data. This includes the in-flight calibration and validation of the data, followed by retrieval of reflected solar and Earth-emitted radiation fluxes at the top of the atmosphere TOA. Atmospheric temperature and humidity profiles from the Global Meteorological Assimilation Office of Goddard Space Flight Center are used with these TOA fluxes to compute radiation fluxes at the surface and at selected levels in the atmosphere. These fluxes for individual pixels are then spatially averaged over one degree latitude by one degree longitude grid regions at the time of overpass. Finally, data from geosynchronous meteorological satellites are ingested to give information to interpolate in time between RBI measurements.