ATMOS ATLAS-3 Mission Solar Spectra Directory Architecture: README - this file header.info - reference header information pat3.f03ss.sun - spectrum pat3.f04ss.sun - spectrum pat3.f09ss.sun - spectrum pat3.f12ss.sun - spectrum Introduction: Following the first flight of the ATMOS instrument on Spacelab 3, the first high resolution infrared solar spectra were published covering the 2 - 16 wavelengths. The last shuttle flight of the ATMOS instrument provided a significantly larger number of observation opportunities from which a much higher signal-to-noise ratio average solar spectra have been created (see Abrams, et al, 1996). These averages are available through ftp to thunder.jpl.nasa.gov/atmos/at3.solar or can be requested on cd-rom. Data Description: The full ATMOS sensor response (600-4800 cm-1) is limited to smaller spectral intervals by optical bandpass filters, of which solar averages have been created from the following regions: Filter # Bandpass ------------------------ 12 600 - 1400 9 600 - 2450 3 1580 - 3350 4 3150 - 4800 ------------------------- The spectra are labeled 'at3.fXss.sun', where X corresponds to 12, 9, 3, or 4 as in the above table. 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 find these examples of ATMOS ATLAS-3 solar spectra by anonymous ftp to thunder.jpl.nasa.gov/atmos/level1 Go back to the previous page. File modified by: A. Chang 3-16-98 / Links updated by Bill Irion 3/19/01.