The Next Generation of Active Cavity Radiometers for Space-Based Remote Sensing
Joseph P. Rice, Steven R. Lorentz, T M. Jung
Active cavity radiometers (ACRs) have been used for years to measure solar radiation and Earth radiation from low Earth orbit. Extant space-flight ACRs were designed to measure relatively high irradiance values, approximately 136 mW/cm2 for total solar irradiance missions (Crommelynck 1984, Brusa 1986, Willson 1979) and 40 mW/cm2 for Earth radiation from low earth orbit (Luther 1986). Future ACR missions that are being proposed involve, for example, monitoring Earth radiation from L1 orbit, monitoring total solar irradiance changes at part per million levels, and adding filters in front of ACRS to obtain spectral selectivity. These missions motivate ACR designs that either have much higher resolution or are capable of measuring orders of magnitude lower irradiance values than those referred to above. For example, near L1 (about 1.5 x 105 km towards the sun) the total irradiance from the full Earth disk can be estimated within an order of magnitude to be about 1 5W/cm2, where about 2/3 is solar reflected and about 1/3 is thermally emitted. This is more than 104 times lower than the typical irradiance values measured by extant space-flight ACRs. Such low irradiance levels (and lower) are rountinely measured with accuracy using cryogenic ACRs at national standards laboratories to implement and maintain detector-based radiometric scales. Examples at the National Institute of Standards and Technologly (NIST) include a liquid-helium-cooled ACR (Lorentz 1993) and a liquid-nitrogen-cooled ACR that has been demonstrated and is under development (Rice 1998). However, reliable, long-term space-flight instruments are often required to be non-cryogenic, with operating temperatures in the range of approximately -100C to +600C. Achieving reasonable signal/noise ratios for measurements of such low irradiance values with a non-cryogenic ACR presents a challenging. Though solvable problem.
10th Conference on Atmospheric Radiation
June 28-July 1, 1999
Madison, WI, USA
active cavity radiometer, remote sensing
, Lorentz, S.
and Jung, T.
The Next Generation of Active Cavity Radiometers for Space-Based Remote Sensing, 10th Conference on Atmospheric Radiation, Madison, WI, USA
(Accessed June 3, 2023)