4.2 NISTAR

The NISTAR radiometer is shown in Figure 10 and described in detail in Appendix B. It is a 4-channel radiometer. Three of those channels are absolute cavities and the fourth is a silicon photodiode radiometer. The instrument views the sunlit Earth continuously to obtain Earth radiation data from 0.2 to 100 µm in 4 wavelength bands. An accuracy of 0.1% is expected. The accuracy goal is based on the high sensitivity of the instrument and on the ability to integrate for long times (minutes) due to the deep space location. The spectral channels are:

1. A visible to far infrared (0.2 to 100 µm) channel to measure total radiant power in the UV, visible, and infrared wavelengths.
2. A solar (0.2 to 4 µm) channel to measure reflected solar radiance in the UV, visible and near infrared wavelengths.
3. A near infrared (0.7 to 4 µm) channel to measure reflected IR solar radiance.
4. A photodiode (0.3 to 1 µm) channel for calibration reference for the spectroradiometer.

Figure 10 View of the Scripps-NISTAR multi-channel absolute radiometer.