For the 1984-2003 ERBS data sets, it is estimated that the calibrated ERBE earth-reflected TSI measurements have precisions approaching 0.2 Watts-per-squared-meter at satellite altitudes. In this paper, for each of the ERBS, NOAA-9, and NOAA-10 Spacecraft platforms, the solar calibrations of the ERBE sensor responses are described as well as the derived ERBE sensor response changes as a function of TSI exposure time. The NOAA-9 and NOAA-10 ACR responses decreased as much as 10% due to higher integrated TSI exposure times.
To estimate the 1999-2004, ERBS sensor response changes, the 1984-1997 NOAA-9, and 1986-1995 NOAA-10 Spacecraft ERBE ACR responses were used to characterize response changes as a function of exposure time. On October 6, 1999, the on-board ERBS calibration systems failed. During the October 1984 through September 1999 period, the ERBS shortwave sensor responses were found to decrease as much as 8.8% when the quartz filter transmittances decreased due to direct exposure to TSI. Using on-board calibration systems, 1984 through 1999, long-term ERBS/ERBE ACR sensor response changes were determined from direct observations of the incoming TSI in the 0.2-5 micrometer shortwave broadband spectral region. The earth-reflected total solar irradiances were measured using broadband shortwave fused, waterless quartz (Suprasil) filters and ACR’s that were covered with a black paint absorbing surface. During the October 1984 through September 2004 period, the NASA Earth Radiation Budget Satellite (ERBS)/ERBE nonscanning active cavity radiometers (ACR) were used to monitor long-term changes in the earth radiation budget components of the incoming total solar irradiance (TSI), earth-reflected TSI, and earth-emitted outgoing longwave radiation (OLR). The NASA Earth Radiation Budget Experiment (ERBE) missions were designed to monitor long-term changes in the earth radiation budget components which may cause climate changes. Finally, we discuss efforts underway to combine GPS space-based observations of plasmaspheric TEC, with ground-based magnetometer measurements, and satellite-based images from NASA's IMAGE satellite, to produce new dynamic models of the plasmasphere. We will discuss a new data assimilation model of ionosphere, the Global Assimilative Ionosphere Model (GAIM), capable of integrating measurements from GPS and other sensors with a physics-based ionospheric model, to provide detailed global nowcasts of ionospheric structure, useful for science and applications. New flight hardware designs are being developed that permit simultaneous measurement of integrated electron content along new raypath orientations, including zenith, cross-track and nadir antenna orientations (the latter via bistatic reflection of the GPS signal off ocean surfaces). Complementary measurements from space-borne GPS receivers in low-Earth orbit provide information on both vertical and horizontal structure of the ionosphere/plasmasphere system. Data available from thousands of ground-based GPS receivers are used to image the large-scale and mesoscale ionospheric response to geospace forcings at high-precision covering all local times and latitudes.
This simple observable is yielding a wealth of new scientific information about ionosphere and plasmasphere dynamics. Transmissions of the Global Positioning System (GPS) satellites can be used to measure the total electron content (TEC) between a receiver and several GPS satellites in view.
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