Detectors and focal plane modules for weather instruments

Weather satellite instruments require detectors with a variety of wavelengths ranging from the visible to VLWIR. The Cross-track infrared Sounder (CrIS) is a Polar Orbiting interferometric sensor that measures earth radiances at high spectral resolution, using the data to provide pressure, temperature and moisture profiles of the atmosphere. The pressure, temperature and moisture sounding data are used in weather prediction models that track storms, predict levels of precipitation etc. The CrIS instrument contains SWIR (λ c ~ 5 μm at 98 K), MWIR (λ c ~ 9 μm at 98 K) and LWIRs (λ c ~ 15.4 μm at 81 K) bands in three Focal Plane Array Assemblies (FPAAs). CrIS detectors are 850 μm diameter detectors with each FPAA consisting of nine photovoltaic detectors arranged in a 3 x 3 pattern. Molecular beam epitaxy (MBE)-grown Hg 1-x Cd x Te material are used for the detectors fabricated in a modified Double Layer Planar Heterostructure (DLPH) architecture. Each detector has an accompanying cold preamplifier. SWIR and MWIR FPAAs operate at 98 K and the LWIR FPAA at 81 K, permitting the use of passive radiators to cool the detectors. D* requirements at peak 14.01 μm wavelength are ≥ 5.0E+10 Jones for LWIR, ≥ 7.5E+10 Jones at 8.26 μm for MWIR and ≥ 3.0E+11 Jones at peak 4.64 μm wavelength for SWIR. All FPAAs exceeded the D* requirements. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 10 10 cm-Hz 1/2 /W at 14.0 μm, 9.6 x 10 10 cm-Hz 1/2 /W at 8.0 μm and 3.4 x 10 11 cm-Hz 1/2 /W at 4.64 μm.