ATMOS Spacelab 3 Mission Solar Spectra Directory Architecture: README-this file header.info - reference header information psl3.sun.1 - spectrum psl3.sun.2 - spectrum psl3.sun.3 - spectrum psl3.sun.4 - spectrum psl3.sun.sr02 - spectrum psl3.sun.sr04 - spectrum psl3.sun.sr05 - spectrum psl3.sun.sr06 - spectrum You can ftp these examples of ATMOS Spacelab 3 solar spectra by anonymous ftp to thunder.jpl.nasa.gov/atmos/sl3.solar References: C. B. Farmer and R. H. Norton, "Atlas of the Infrared Spectrum of the Sun and the Earth Atmosphere from Space. Volume I, The Sun", NASA Reference Publication 1224, 1989. C. B. Farmer and R. H. Norton, "Atlas of the Infrared Spectrum of the Sun and the Earth Atmosphere from Space. Volume II, Stratosphere and Mesosphere, 650 to 3350 cm-1 ", NASA Reference Publication 1224, 1989. M. Geller, "Atlas of the Infrared Spectrum of the Sun and the Earth Atmosphere from Space. Volume III, Key to Identification of Solar Features", NASA Reference Publication 1224, 1989. C. B. Farmer, "The ATMOS Solar Atlas", Infrared Solar Physics, 511-521, 1994. Introduction: High resolution infrared spectra of the sun have been obtained by the ATMOS instrument, a Fourier transform spectrometer, from low Earth orbit while flying on the Space Shuttle. After the first flight of the instrument in 1985, an atlas of plots of the solar spectra was published (Farmer and Norton, 1989) with the intent that this be followed up by CD-ROM of the same data. Users are encouraged to read the introduction in this and other volumes for an extended description of the data. Due to unforseen circumstances, a CD-ROM of that data has not yet been created with all of the necessary supporting software or descriptive files. The purpose of this CD-ROM/ftp-directory is to provide general users with the 'raw' spectral data in a computer compatible format. Data Description: The full spectral response of the ATMOS instrument (600 to 4800 cm-1) is broken down into smaller band passes by the use of four optical filters. Filter # Bandpass ------------------------ 1 600 - 1180 2 1100 - 2000 3 1580 - 3350 4 3150 - 4800 ------------------------- There are eight unapodized spectra in binary (Fortran integer*2 or 16-bit words) files, each of which has been arbitrarily normalized to a peak value of 30000. The spectra are labelled sl3.sun.X, for the Spacelab 3 mission solar spectra, and X for the filter number or occultation. Averages of a large number of high sun spectra were possible from ATMOS observations made near orbital sunsets. These are simply denoted by a number at the end of the spectrum name according to filter. For contrast, and as an aid to identifying ATMOS instrument absorption features, averages made from spectra obtained around single orbital sunsrise are also supplied. These are of poorer signal-to-noise ratios. The designations correspond as follows: Occultation name Filter ------------------------- sr02 3 sr04 4 sr05 2 sr06 1 ------------------------ Data Format: Each spectrum file is a 1-D binary array of 2-byte signed integers (big endian: hi-byte, lo-byte). The number of points (Num_Pts below) is thus 0.5 * the file size in bytes. On a MAC or Sun, these can be read directly to an integer array, using for example, a C fread() routine. On a DEC or PC, a byte swap would have to be performed following the read operation. (In FORTRAN the process is more complicated because the data is pure binary and has no record terminators.) Important ancillary information necessary to recreate the frequency scale are provided in the file "header.info". For each spectrum the following information is given in a single line: Field Contents ================= ================================================= Run_ID Run label, (yymmddhhmmss), giving GMT of measurement optionally preceeded by an "r" for a ratioed spectrum. Spectrum file name is this Run ID preceeded with a "p". Filt ATMOS optical filter number (1-13) Locat Observation location or mission name F/R Forward/reverse instrument scan Alias Alias number (1 or 2) Loc_Mx Index of maximum spectral point Num_Intf Number of interferogram points N_Fring Number of laser fringes FFT_sz Fourier transform size I_First Index of first point saved Num_Pts Number of points in file Step Step size in fringes, between successive interferogram samples SP_Max Maximum value of spectrum ZPD_GMT GMT of ZPD point (seconds since midnight), transformed to give run label Obs_Alt Observation altitude (km) Obs_Lat Observation latitude (decimal degrees) Obs_Lon Observation longitude (decimal degrees) Tan_Ht Tangent height (km) - derived from data TP_Lat Tangent point latitude (decimal degrees) - calculated TP_Lon Tangent point longitude (decimal degrees) - calculated Tan_Pres Retrieved tangent pressure (bars) - derived from data Pres_Err Retrieved tangent pressure error (bars) FOV_Mag Magnification for internal field of view (constant for ATMOS at 2.7) Ext_FOV External field of view (mrad), variable according to optical filter used SC_Dopp Estimated spacecraft doppler shift along line of sight Las_Sem_Frq Laser semi-frequency (cm-1) Frq_Cor_Fac Instrument line frequency correction Sc_Factor Rescaling factor to convert integer spectral values to real Start_Frq Approx. starting frequencies for spectrum (cm-1) End_Frq Approx. ending frequencies for spectrum (cm-1) Comments Comments, usually the occultation name The file can be read using the following read and format statements: read (20,810) runlabl,afilter,obsloc,forrev, & aalias,mxpptloc,numint,afring,afftsiz,afirst, & numprim,step,spmaxval,zpdgmt,obsalt,latitude, & longtude,tanht,tplat,tplon,tanpres,preserr, & fovmag,extfov,scdopp,lasemfrq,wifact, & spec_x_fac,sig0,sig1,acomment 810 format(a16,2x,a2,2x,a8,1x,a2,i5,i9,i9,i8,i8,i8,i8,f6.1,f10.5, & f11.2,f9.3,f8.2,f9.2,f9.3,f8.2,f9.2,2x,e10.4,2x,e11.4, & f9.2,f7.3,2x,e11.4,f11.4,f14.9,e11.4,f11.4,f11.4,2x,a72) Data Scaling: The spectra are stored as an integer array to conserve space. The spectral points can be rescaled to their original values by multiplying by Sc_Factor. Frequency Scaling: The frequency interval between successive points is determined from, Freq_Int = Corr * Las_Sem_Frq / (Step *FFT_sz) where the correction factor, Corr, is very nearly 1.0., e.g. Freq_Int = 7899.0015/(2.0*524288) = 0.0075331 cm-1. The frequency corresponding to each spectral point is found using, freq[i] = Freq_Int * [ (i - 1) + (I_First - 1) + FFT_sz*(Alias - 1) ] where array indices are assumed to start at 1 (not 0). For greater accuracy, the frequency interval can be corrected by Frq_Cor_Fac * (1 + SC_Dopp) Corr = -------------------------------------------------------- [1 - (Ext_FOV/1000)*(Ext_FOV/1000)*(FOV_Mag)*(FOV_Mag)/16] Acknowledgements - This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. You can ftp these examples of ATMOS Spacelab 3 solar spectra by anonymous ftp to thunder.jpl.nasa.gov/atmos/sl3.solar Go back to the previous page. File modified by: A. Chang 3-16-98 / Links updated by Bill Irion 3/19/01