The High-spectral resolution Interferometer Sounder (HIS) covers the 3.1-17 micron spectral region and has a resolution of approximately 0.5cm-1 from 600-1100 cm-1 (9.1-16.7 micron) and 1.0 cm-1 resolution from 1100-2700 cm-1(3.7-9.1 micron).
The aircraft HIS is a Fourier Transform spectrometer which views directly downward through an open port in a pod mounted under the center line of the fuselage. From altitude (approximately 20 km) it's instantaneous field of view is 2 km directly below the plane. Calibration is accomplished by viewing two high emissivity blackbodies, servo-controlled to 300K and 240K. A linear plane mirror Michelson interferometer provides double-sided interferograms in both scan directions. It's auto-alignment system makes it possible to operate in the ambient thermal environmnent of the pod and in very close proximity to the aircraft jet engine. The optical bench is shock-mounted to dampen high-frequency vibration, and the interferometer is evacuated to protect the beamsplitter during descent. The three spectral bands covering most of the region from 3.8 to 16.6 micron are split inside a single liquid helium dewar, which contains three sets of bandpass cold filters, focusing optics and arsenic-doped silicon detectors.
Accuracy: 0.5 degrees brightness temperature at 260K
Precision: 0.2 degrees brightness temperature at 260 K.
References:
Ackerman, S. A., W.L. Smith, J. Spinhirne, and H.E. Revercomb, 1990: The 27-28 October 1986 FIRE IFO Cirrus Case Study: Spectral Properties of Cirrus Clouds in the 8-12 micron Window, Monthly Weather Review, 118, 2377-2388.
Smith, W. L., X L. Ma, S. A. Ackerman, H. E. Revercomb, R. O. Knuteson, 1992: Remote sensing cloud properties from high-spectral resolution infrared observations, J. Atmos. Sci., 50, 1708-1720.
Smith, W.L., H.M. Woolf, and H.E. Revercomb, 1991: A Linear Simultaneous Solution for Temperature and Absorbing Constituent Profiles from Radiance Spectra", Applied Optics, 30, 1117-1123.
Revercomb, H. E. ,H. Buijs, H.B. Howell, D.D. LaPorte, W.L. Smith, and L.A. Sromovsky, 1988: Radiometric Calibration of IR Fourier Transform Spectrometers: Solution to a Problem with the High Resolution Interferometer Sounder", Applied Optics, 27, 3210-3218.
The MODIS Airborne Simulator (MAS), a scanning spectometer built by Daedalus Enterprises, Inc. for NASA's Goddard Space Flight Center and Ames Research Center, is used for measuring reflected solar and emitted thermal radiation in 50 narrowband channels between 0.55 and 14.2 microns. The instrument provides multispectral images of outgoing radiation for developing and validating algorithms for the remote sensing of cloud, aerosol, water vapor, and surface properties from space. The spectrometer scans a swath width of 37 km (p/m 43 degrees about nadir), perpendicular to the aircraft flight track, with a 2.5 mrad instantaneous field of view. Images are thereby produced with a spatial resolution of 50 m at nadir from a nominal aircraft altitude of 20 km. Nineteen of the spectral bands correspond closely to comparable bands of the Moderate Resolution Imaging Spectroradiometer (MODIS), a facility instrument being developed for EOS to be launched in the late 1990s.
Since it's first deployment in the FIRE cirrus campaign (November 1991), MAS has flown in many field experiment throughout the world, providing critical data sets for assessing the scientific capability and usefulness of MODIS channels. In addition, with it's high spatial resolution MAS is able to provide unique information on the small-scale distribution of various geophysical parameters.
References
Gumley, L. E., and M. D. King, 1995: Remote sensing of flooding in the U.S. upper midwest during the summer of 1993. Bull. Amer. Meteor. Soc., 76, 933-943.
King, M.D., W. P. Menzel, P. S. Grant, J. S. Myers, G. T. Arnold, S. E. Platnick, L. E. Gumley, S. C. Tsay, C. C. Moeller, M. Fitzgerald, K. S. Brown and F. G. Osterwisch, 1995: Airborne scanning spectrometer for remote sensing of cloud, aerosol, water vapor and surface properties, J. Atmos .Ocean. Tech, in press.
The Cloud Lidar System (CLS) is an active, elastic-scatter laser radar instrument. The CLS has flown on the ER-2 aircraft sinc 1983 for participation in cloud radiation and severe storm filed experiments. The instrument provides the true height of cloud boundaries and the density structure through optically less dense clouds. The height structure of cirrus, cloud-top density, multiple cloud layers are uniquely measured. Aerosol layers may also be profiled.
The Goddard CLS is a compact automated instrument that was designed to operate from a high-altitude research aircraft in order that measurements can be obtained from above the highest clouds. The transmitter for the lidar system is a Nd:YAG laser which has a 0.1 J pulse energy at the wavelength of 532 nm. Backscattered light is collected by an 18-cm telescope and is split by a polarization beamsplitter; the parrallel and perpendicular components are separately detected and recorded. Logarithmic signal amplifiers are employed to accommadate the large signal dynamic range. The current pulse repetition rate of the laser is 10 Hz, and at the nominal 200 m per sec aircraft flight speed measurement are acquired at a 20 m interval along the flight path..
References
Spinhirne, J. D., M. Z. Hansen and L. O. Caudill, 1982: Cloud top remote sensing by airborne lidar, Appl. Opt., 21, 1564.
Spinhirne, J. D. and W. D. Hart, 1990: Cirrus structure and radiative parameters from airborne lidar and spectral radiometer observations, Mon. Wea. Rev., 2329.