UWITRA93.DOC Version 2.0 29 August 1993 ROK This file describes the infrared spectral data and temperature and moisture profiles provided by the University of Wisconsin to the ITRA line-by-line intercomparison (1993). The High-resolution Interferometer Sounder (HIS) is a Fourier Transform Spectrometer (FTS) which uses laser controlled sampling and on-board blackbodies to achieve highly accurate wavelength and spectral radiance absolute calibration. The HIS data described below was collected under United States and State of Wisconsin funded projects lead by Principal Investigator William L. Smith, Professor of Meteorology, and Director of the Cooperative Institute for Meterological Satellite Studies at the University of Wisconsin -- Madison. The scientist responsible for the HIS instrument development and calibration is Dr. Henry E. Revercomb also of the University of Wisconsin -- Madison. The HIS data are unapodized and the interferometer finite field of view effect has been removed. All wavenumbers listed in the following tables are in reciprocal centimeters (cm-1). Only the data within the optical filter bandpass has been included in the HIS data files. Also, the large number of points in the balloon sonde data from the CLASS sondes (400-500) has been reduced to 50 profile points spanning the range of pressures measured. The file 14AP1800.TXT containing the raob data for April 14th deserves special mention since it is composed of a time and space average of NWS radiosondes which make the characterization of the atmosphere much more uncertain for that case. Only measured data has been provided. This means that some quantities must default to their climatic means. DATA FILES: (See CONTENTS.DOC for further information) NAMING CONVENTION: HIS104 -- 14 APRIL 1986 (HIS on NASA ER-2 Aircraft during TEST FLIGHT) HIS1MR -- 1 MARCH 1992 (HIS on NASA ER-2 Aircraft during STORMFEST) GPXO31 -- 31 OCTOBER 1988 (Ground-Based Atmospheric Profiling Experiment) GPXN01 -- 1 NOVEMBER 1988 (Ground-Based Atmospheric Profiling Experiment) HIS OBSERVATIONAL BAND LIMITS: BAND 1 : 600 - 1080 CM-1 BAND 2 : 1080 - 1850 CM-1 BAND 3 : 2000 - 2600 CM-1 (Band 3 not available for GAPEX data) ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- IMPORTANT INFORMATION ABOUT THE HIS DATA PROVIDED IN UWITRA93. ---------------------------------------------------------------------------- WAVENUMBER SCALE OF HIS DATA: The wavenumber scale of the HIS data is determined by an on-board HeNe laser. For UWITRA93 the laser wavenumber has been assumed to be 15799.00 cm-1. A numerical filter applies a reduction factor (R=14,8,8 for bands 1,2,3) to the observed data which defines a starting (or reference) wavenumber for each HIS band. The reference wavenumbers which correspond to the laser wavenumber 15799.00 cm-1 are 564.25 cm-1, 987.4375 cm-1, and 1974.875 cm-1 for bands 1, 2, and 3, respectively. The point spacing of the output data also depends on the laser wavenumber assumed and the reduction factor appropriate for each HIS band. In addition, the point spacing in wavenumber depends on the number of points used in the FFT to transform from the Fourier domain to the spectral domain. The difference in point spacing between the Band 2 uplooking and downlooking observed data is due to using 2048 points versus 1024 points in the data processing. SPECTRAL RESOLUTION OF HIS DATA: Spectral resolution here refers to the information content of the observation and is always equal to (minimally sampled) or greater than (oversampled) the data's point spacing in wavenumber. Since the instrument used to obtain the observation is a Fourier Transform Spectrometer, the spectral resolution is defined in terms of the maximum Optical Path Difference of the measurement. Since the HeNe laser is used to define the optical path difference, the maximum OPD as well as the spectral resolution depends on the assumed laser wavenumber. The differences in spectral resolution between HIS bands and from one observation to the next reflect different choices made during data processing; the same instrument hardware was used to make all the observations in UWITRA93. RADIOMETRIC CALIBRATION OF HIS DATA: All the HIS data was calibrated using a two point calibration scheme whereby periodic views of hot and cold reference sources are used to remove the background contributions of the instrument. In flight configuration two high precision cavity blackbodies are used as reference sources. During surface operations, the cold reference target is replaced with an open mouthed dewar of liquid nitrogen. Note especially that the HIS instrument operates in ambient air, that is the path between the calibration reference sources and the interferometer contains both CO2 and H2O normal atmospheric concentrations. This means that certain individual channels, e.g. near 667 cm-1, 1500 cm-1, and 2380 cm-1, can be "blinded" by very opaque absorption near the instrument. The result is that these few channels appear anomolous (spikes) because they are much noisier than less opaque channels nearby. In particular, the HIS calibration is undefined in the narrow spectral range 667.016 to 669.771 cm-1. This narrow region should *not* be used for spectroscopic comparisons. ---------------------------------------------------------- POINT SPACING OF HIS DATA (CM**-1) [DVspacing = VLASER/(2*R*N)] ---------------------------------------------------------- DATA BAND 1 BAND 2 BAND 3 ---------------------------------------------------------- HIS104 0.2755127 0.4821472 0.4821472 HIS1MR 0.2755127 0.4821472 0.4821472 GPXO31 0.2755127 0.9642944 GPXN01 0.2755127 0.9642944 ---------------------------------------------------------- ---------------------------------------------------------- SPECTRAL RESOLUTION (UNAPODIZED) (CM**-1) [DVres = 1./(2.*X)] ---------------------------------------------------------- DATA BAND 1 BAND 2 BAND 3 ---------------------------------------------------------- HIS104 0.3640322 0.6370564 0.6370564 HIS1MR 0.3224285 0.6809913 0.9642944 GPXO31 0.3640322 0.9642944 GPXN01 0.3640322 0.9642944 ---------------------------------------------------------- ---------------------------------------------------------- MAXIMUM OPTICAL PATH DIFFERENCE (CM) [X = DX * DSPTS / 2.] ---------------------------------------------------------- DATA BAND 1 BAND 2 BAND 3 ---------------------------------------------------------- HIS104 1.373505 0.7848598 0.7848598 HIS1MR 1.550731 0.7342236 0.5185138 GPXO31 1.373505 0.5185138 GPXN01 1.373505 0.5185138 ---------------------------------------------------------- ---------------------------------------------------------- NUMBER OF POINTS USED IN DOUBLE SIDED INTERFEROGRAM (DSPTS) [Exclusive of ZPD] ---------------------------------------------------------- DATA BAND 1 BAND 2 BAND 3 ---------------------------------------------------------- HIS104 3100 3100 3100 HIS1MR 3500 2900 2048 GPXO31 3100 2048 GPXN01 3100 2048 DX 8.861320E-4 5.063612E-4 5.063612e-4 ---------------------------------------------------------- Please refer questions about HIS data to: Robert O. Knuteson Cooperative Institute for Meterological Satellite Studies University of Wisconsin -- Madison 1225 W. Dayton Madison, WI 53706 USA phone (608-263-4085) fax (608-262-5974) email (bobk@ssecmail.ssec.wisc.edu)