CRYOGENIC RADIOMETERS FOR REMOTE-SENSING AND PYRHELIOMETRY

Liquid-helium cooling of electrical substitution radiometers (ESRs) offers significant improvements in the time constant and sensitivity of these spectrally flat receivers. These cryogenic improvements have been used to good advantage in the design and prototype construction of fast ESR receivers (and receiver arrays) with sufficient sensitivity for NASA Earth remote-sensing applications. We describe some of our results in this area and suggest how the advantages offered by cryogenic ESRs might be useful in achieving the very long-term reproducibility that will be required in 21st-century pyrheliometry.