This is a description of the contents of the GENESIS Level 2 "txt" data. ============================================================ SUMMARY ============================================================ The Genesis GPS Occultation Observations Level 2 data set contains profiles of atmospheric temperature, pressure, refractivity, and water vapor pressure with resolution of about a kilometer, derived from LEO-GPS (low-earth-orbiter satellites and satellites of the Global Positioning System) radio occultation (limb sounding) data. Similar profiles from NCEP and ECMWF analyses are also included. LEOs collecting occultation data include GFZ's CHAMP (CHallenging Minisatellite Payload satellite) and CONAE's SAC-C. These are the Level 2 products of this radio occultation data set. The full set of products available include * Level 0: Raw GPS data * GPS data for orbit determination in RINEX format * Orbit products * Level 1A: Atmospheric phase delay and signal amplitude * Level 1B: Atmospheric doppler shift and bending * Level 2: Atmospheric refractivity, temperature, pressure, water vapor pressure profiles, and comparisons to weather analysis and radiosondes. CHAMP and SAC-C each carry a JPL Blackjack GPS receiver and a rearward-facing antenna to record the signals of GPS satellites setting behind the Earth's limb as the signal passes through the atmosphere. (SAC-C also carries a forward-facing antenna, currently inactive.) Typically over 200 of these "occultations" occur per day per LEO with fairly uniform global distribution. By measuring the precise phase delay experienced by the GPS signals, and using precise clock-offset and orbit information, the atmospheric component of the phase delay can be extracted. Assuming local spherical symmetry about the tangent point, inversion of the atmospheric phase delay phase measurements during an occultation yields atmospheric refractivity profiles, which can be converted to temperature and pressure profiles between 60 km and the middle troposphere, and, with independent knowledge of temperature, into water vapor density in the middle and lower troposphere. Valuable properties of radio occultation measurements of atmospheric profiles include: * Self-calibrating, making them ideal for climate detection. * Sub-kilometer vertical resolution. * Sub-Kelvin temperature accuracy below 45 km. * All-weather operation * Independent height and pressure data allowing computation of geopotential heights and derived wind fields * Concurrent global coverage with a small constellation Comparison of CHAMP and SAC-C to National Center for Environmental Prediction (NCEP) and the European Center for Medium-range Weather Forecast (ECMWF) analyses show that GPS occultation temperature profiles are consistent with the models to better than 0.5 K in the mean, and better than 1.5 K in standard deviation. ============================================================ See README_genesis.txt for general description of GENESIS txt format. ============================================================ Following is the metadata header of an L2 txt file interleaved with commentary. Metadata are largely identical or similar to L1A and L1B files (see README.L1a.txt and README.L1b.txt for further commentary). ============================================================ ProductCreationTime = 2002-01-12T00:10:52 ShortName = GPS-OCC-L2 LongName = GPS-Occultation-Level-2 DataSetID = 20011029_0603sac_g46_1p0 ParameterName = {"Atmosphere", "Refractivity", "Temperature", "Pressure" , "Water Vapor Pressure"} PlatformShortName = SACC SensorShortName = SACC-BlackJack VersionID = 1.0 ProcessingLevel = 2 GranulePointer = 20011029_0603sac_g46_1p0.L2.txt TextFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L2/txt/20011029_0603sac_g46_1p0.L2.txt XmlFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L2/xml/20011029_0603sac_g46_1p0.L2.xml HdfFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L2/hdf/20011029_0603sac_g46_1p0.L2.hdf WestBoundingCoordinate = 290.578668 NorthBoundingCoordinate = -63.698545 EastBoundingCoordinate = 291.674349 SouthBoundingCoordinate = -64.865289 RangeBeginningDate = 2001-10-29 RangeBeginningTime = 06:03:27.500 RangeEndingDate = 2001-10-29 RangeEndingTime = 06:04:41.480 Transmitter = gps46 Receiver = sacc ReferenceTransmitter = gps31 ReferenceReceiver = sutm LowestAltitude = 0.217938 LocalTime = 01:28:00 LinkOrientation = -23.40 AS = ON ProcessedFileReference = /genesis/occult/retrievals/sacc/g150c5_q2s/y2001/2001-10-29/2001-10-29-06:03sacc_gps46 AngleToVelocity = 156.3 ErrorFlags = 1111111 DayOfYear = 302 ReceiverSoftwareVersion = TBD DataTypeName = { "SACC-Profile", "NCEP_FNL-Profile" } DataTypeID = { 65, 83 } Fields(65) = { "Height", "Lat", "Lon", "Refractivity", "Temperature", "Pressure" , "WV Pressure"} Fields(83) = { "Height", "Lat", "Lon", "Refractivity", "Temperature", "Pressure" , "WV Pressure"} # Fields for both data types are # Height (km) # Lat (degrees) # Lon (east longitude, degrees) # Refractivity # Temperature (K) # Pressure (mbar) # WV Pressure (water vapor pressure, mbar) StartTimeInSecondsFromJ2000 = 0.5760740750000000E+08 TimeForRadiusOfCurvatureFromJ2000 = 0.5760744100000000E+08 RadiusOfCurvature = 0.6394583273697736E+04 CenterOfCurvature = { 0.2222355413784953E+00, 0.3872670465589181E+00, 0.3773061614997096E+02 } CA_StartPhase = 0.27790739E-01 CA_EndPhase = 0.22948012E+01 CA_MinimumPhase = 0.27789204E-01 CA_MaximumPhase = 0.22948012E+01 CA_StartSNR = 0.67462666E+03 CA_EndSNR = 0.11722047E+02 CA_MinimumSNR = 0.83728909E+00 CA_MaximumSNR = 0.74218067E+03 P2_StartPhase = 0.46402915E-01 P2_EndPhase = 0.21985969E+01 P2_MinimumPhase = 0.46402915E-01 P2_MaximumPhase = 0.21985969E+01 P2_StartSNR = 0.96000000E+02 P2_EndSNR = 0.00000000E+00 P2_MinimumSNR = 0.00000000E+00 P2_MaximumSNR = 0.11600000E+03 83 0.2179380810E+00 -.6369854460E+02 -.6937615900E+02 0.2916927330E+03 0.2714624795E+03 0.9547654943E+03 0.3701643200E+01 65 0.2179380810E+00 -.6369854460E+02 -.6937615900E+02 0.2986856280E+03 0.2662004660E+03 0.9498059320E+03 0.5368842820E+01