This is a description of the contents of the GENESIS Level 1B "txt" data.

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SUMMARY

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The Genesis GPS Occultation Observations Level 1B data set consists of
LEO-GPS (low-earth-orbiter satellites and Global Positioning System
satellites) radio occultation (limb sounding) atmospheric doppler and
bending data for use in computing atmospheric refractivity, temperature,
pressure, and water vapor profiles.  LEOs collecting occultation data
include GFZ's CHAMP (CHallenging Minisatellite Payload satellite) and
CONAE's SAC-C. Data are available at the two GPS frequencies, 1.2 and
1.6 GHz, at a time resolution of 1 second or better.  These are the
Level 1B 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.

Smoothed atmospheric doppler and bending angle are useful intermediate
products between the Levels 1A and 2 products.  These products are
provided at a sample rate of 1/sec or better for the 1.6 GHz frequency,
and at a rate of 1/sec for the 1.2 GHz frequency.  The 1.2 GHz data has
lower SNR than the 1.6 GHZ data, and is used to subtract the effect of
the ionosphere.  Atmospheric bending with the effect of the ionosphere
removed, and impact parameter are also provided.  Bending angle and impact
parameter are computing assuming local spherical symmetry.

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See README_genesis.txt for general description of GENESIS txt format.

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Following is the metadata header of an L1B txt file interleaved with commentary.
Metadata are largely identical or similar to L1A (see README.L1a.txt for further commentary).

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ProductCreationTime = 2002-01-12T00:10:52
ShortName = GPS-OCC-L1B
LongName = GPS-Occultation-Level-1B
DataSetID = 20011029_0603sac_g46_1p0
ParameterName = {"Atmosphere", "SmoothedPhaseDelay", "SmoothedPhaseSNR", "DopplerShift", "Bending"}
PlatformShortName = SACC
SensorShortName = SACC-BlackJack
VersionID = 1.0
ProcessingLevel = 1B
GranulePointer = 20011029_0603sac_g46_1p0.L1b.txt
TextFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L1b/txt/20011029_0603sac_g46_1p0.L1b.txt
XmlFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L1b/xml/20011029_0603sac_g46_1p0.L1b.xml
HdfFilePointer = ftp://sideshow.jpl.nasa.gov/pub/genesis/glevels/sacc/1p0/y2001/2001-10-29/L1b/hdf/20011029_0603sac_g46_1p0.L1b.hdf
WestBoundingCoordinate = 291.11
NorthBoundingCoordinate = -63.06
EastBoundingCoordinate = 291.12
SouthBoundingCoordinate = -63.07
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
LocalTime = 01:28:00 
LinkOrientation = -23.40
AS = ON 
CalibrationFileReference = /genesis/occult/calibration/sacc/g150c5_q/y2001/2001-10-29/2001-10-29-06:03sacc_gps46
AngleToVelocity = 156.3
ErrorFlags = 1111111
DayOfYear = 302 
ReceiverSoftwareVersion = TBD

DataTypeName = { "CaFine_L1B", "CaCoarse_L1B", "L2Coarse_L1B", "IonFree_L1B" }
DataTypeID = { 21, 22, 24, 31 }
Fields(21) = { "Time", "TransmitTime", "SmoothedPhase", "AtmosphericDoppler", "AtmosDopplerSigma", "AtmosphericBending", "AtmosBendingSigma", "ImpactParam", "SmoothedSNR", "AveragingTime", "VerticalResolution" }
Fields(22) = { "Time", "TransmitTime", "SmoothedPhase", "AtmosphericDoppler", "AtmosDopplerSigma", "AtmosphericBending", "AtmosBendingSigma", "ImpactParam", "SmoothedSNR", "AveragingTime", "VerticalResolution" }
Fields(24) = { "Time", "TransmitTime", "SmoothedPhase", "AtmosphericDoppler", "AtmosDopplerSigma", "AtmosphericBending", "AtmosBendingSigma", "ImpactParam", "SmoothedSNR", "AveragingTime", "VerticalResolution" }
Fields(31) = { "Time", "AtmosphericBending", "AtmosBendingSigma", "ImpactParam", "VerticalResolution" }

# Definition of data in quasi-tabular numerical data set below:
#
#  Four data types:
#   21 = CaFine_L1B, GPS CA-code atmospheric doppler, bending, and impact parameter data.  Typically has same or finer time resolution than CaCoarse_L1B data type, Level 1B data.
#   22 = CaCoarse_L1B, GPS CA-code atmospheric doppler, bending, and impact parameter data, used in performing ionospheric subtraction, Level 1B data.
#   24 = L2Coarse_L1B, GPS L2 frequency atmospheric doppler, bending, and impact parameter data, used in performing ionospheric subtraction, Level 1B data.
#   31 = IonFree_L1B, GPS atmospheric doppler, bending, and impact parameter data, with ionospheric delay removed, Level 1B data.
#
#  Fields for all data types are
#   Time = Time phase received at receiver (seconds past StartTimeInSecondsFromJ2000)
#   TransmitTime = Time signal was transmitted by transmitter (seconds past StartTimeInSecondsFromJ2000)
#   SmoothedPhase = Atmospheric excess phase delay: compressed from Level 1A type (km) (biased)
#   AtmosphericDoppler = Time rate of change of Smoothed Phase (km/s)
#   AtmosDopplerSigma = Error parameter for AtmosphericDoppler (km/s)
#   AtmosphericBending = Bending angle derived from AtmospericDoppler (radians)
#   AtmosBendingSigma = Error parameter for AtmosphericBending (radians)
#   ImpactParam = Impact parameter (km)
#   VerticalResolution = Vertical interval over which profile is smoothed (km) (zero if unset).

StartTimeInSecondsFromJ2000 = 0.5760740750000000E+08

TimeForRadiusOfCurvatureFromJ2000 = 0.5760744100000000E+08
RadiusOfCurvature = 0.6394583273697736E+04
CenterOfCurvature = { 0.2222355413784953E+00, 0.3872670465589181E+00, 0.3773061614997096E+02 }
# Radius and center of curvature of the surface of the Earth at tangent point at time TimeForRadiusOfCurvatureFromJ2000.
# Time when curvature is computed (secs past J2000)
# Radius (km)
# Center (x,y,z coordinates relative to center-of-earth, km)

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

CA_MAx_Bending = 0.0351958183174482
L2_Max_Bending = 0.00378285125519931
LC_Max_Bending = 2.68238899514635e-06
# Maximum bending for CA, L2, and LC (ionospheric-free combination of CA and L2) (rad)