Technology Development in Support of a Future Earth Observation Nanosatellite-Infrared (EON-IR) Atmospheric Sounder

Hyperspectral infrared sounding of the atmosphere has become a vital element in the observational system for weather forecast prediction at National Weather Prediction (NWP) centers worldwide.  The NASA Atmospheric Infrared Sounder (AIRS) instrument was the pathfinder for the hyperspectral infrared observations and was designed to provide accurate atmospheric temperature and water vapor profile information in support of weather prediction.  AIRS was launched in 2002 and continues to operate well.  The Cross-track Infrared Sounder (CrIS) on the Suomi NPP satellite has successfully continued the AIRS measurement, and was launched in 2011.  CrIS also continues to operate well and additional sensors are planned for launch promising to continue the hyperspectral infrared measurements in support of NWP into the late 2030’s.

The cost of AIRS and CrIS is substantial, and has created the need to explore lower cost alternatives for the post-JPSS era.  Their high cost prevents them from being launched into multiple orbits to improve sampling of the diurnal cycle, or into GEO, although EUMETSAT is planning a GEO IR Sounder to launch in the early 2020’s.

JPL NASA is offering an alternate hyperspectral IR sounder architecture for the future involving CubeSats and NanoSats.  The latest technology in large format focal plane assemblies, wide field optics and active cryocoolers enables a reduction in size, mass and cost of the legacy sounders and offer new configurations.  Lessons learned from AIRS and CrIS indicate that temperature and water vapor sounding in the lower troposphere can be achieved with only the MWIR portion of the spectrum.  LWIR spectra are useful for atmospheric composition and upper troposphere/lower stratosphere (UTLS) temperature and water vapor.  These lessons and technology advancements enable a new architecture for infrared sounders of the future.

JPL has begun development of the CubeSat Infrared Atmospheric Sounder (CIRAS) sponsored by the NASA ESTO InVEST Program.  CIRAS employs only an MWIR spectrometer to achieve lower tropospheric temperature and water vapor profiles, but with comparable spatial, spectral and radiometric sensitivity in this band as AIRS and CrIS.  CIRAS operates from 4.08-5.13 µm with 625 channels and spectral resolution of 1.2-2.0 cm^-1.  CIRAS employs an immersion grating spectrometer making the optics incredibly compact, and HOT-BIRD detectors enabling good uniformity and operability over the large 512 x 640 element focal plane.  The CIRAS is packaged in a 6U CubeSat and uses less than14 W.

JPL has also completed a concept study for an LWIR sounder spectrometer, called the Infrared Composition Atmospheric Sounder (INCAS).  INCAS operates from 8-12 µm with 2000 channels, giving a spectral resolution of 0.4-0.8 cm^-1, with comparable spatial resolution and coverage as the other IR sounders. INCAS may not fit alone in a 6U CubeSat, but when combined with CIRAS, together may fit in a 12 U package.  To complete the full band of AIRS and CrIS would require an additional LWIR sounder operating from 12-15µm.  We are exploring technologies to enable this sensing in a small package, and the idea of using the microwave sensors to substitute for information normally obtained in this band.  The combined CIRAS and INCAS for now would make up the Earth Observation NanoSatellite Infrared (EON-IR), capable of meeting the majority of the requirements of AIRS and CrIS in a CubeSat or SmallSat package.

This presentation will discuss the requirements and state of development of the CIRAS and INCAS and the concept we have developed for EON-IR.  Technology advancements and retrieved product accuracy will also be included.