Geodetic Satellite Exact Repeat Mission

 

The US Navy Geodetic Satellite (Geosat) radar altimeter mission collected approximately 750 million global ocean sea level, wave height, and wind measurements from March, 1985 to January, 1990. Data from the first iteration of Geosat was classified, but an unclassified Exact Repeat Mission (ERM) that replicated the initial cycle launched in October, 1986. The ERM ended in 1990, partly due to failures of both on-board tape recorders, but provided more than three years of precise, unclassified altimeter data to the scientific community.

ERM Sensor Data Records (SDR) were originally preserved in 9-track tapes. From 2008 to 2009, 1,098 tapes were recovered with a miniscule loss rate of 0.000172%, preserving these data for continued use in geodetic gravitational modeling and study of fronts and eddies, winds, waves, ice topography, and physical oceanography.

Processing Procedures for 9-Track Tape Recovery

  1. Ship tapes (20–40 per week)
  2. Recover data in tapes, save to DVDs and send DVDs back to NCEI
  3. Check received DVDs and back up
  4. Check data recovery quality
  5. Verify the tape recovery checklist and obtain approval of tape disposal from NCEI
  6. Archive the recovered data

Geosat SDR Recovery Table

Tape Damage Details
Geosat SDR Recovery Table Graphic

Geosat SDR Recovery Table

 

Red number
One block (19 records) lost due to tape damage
Green shading
Data has been fully recovered
White background
Tape is missing because of satellite observation loss
Gray shading
Tape is missing or not shown in the tape inventory

Sensor Data Record (SDR) Data

The Frame Count Check is a quality control effort to quantify record loss.

Legend

Tape-ID of SDRXXYYDDNN
An identification of the data code version (XX), generation year (YY), day (DD) and the tape version (NN)
Original Record#
The number of records count in the data file indicated by the SDR header
Recovered Record#
The total number of recovered records
Loss
The lost number of records count during the data recovery because of tape damage
Early
The frame count of the data record is before the beginning frame count indicated in the header
Late
The data are after the ending frame count in the header
Reverse
The frame count in a data record was before the previous record's frame count
Gap
The frame count jumped by more than 1199, which is a 2-minute gap (1200/10 = 120 seconds = 2 minutes)
Slip
The frame count didn't continue incrementing by 10 (modulo 32), which may indicate an instrument/platform reset or some other problem with the data
Tape Damage Images
Frame Count Check File Graphic

Frame Count Check Files

Data range checks covered all parameters (142 for Header Data, 49 for Record Data) to ensure they fell within the range defined in Tables 1 and 2 of the GEOSAT Interface Control Document (ICD).

Each table or set of tables show the number of records that are out of range, and contains the results of a specific tape shipment to Data Recovery International.

SDR Header Data

Legend

0
Data value is within the data range
-1
Data value is out of the lower bound
1
Data Value is out of upper boundary

Left row shows the parameter numbers corresponding to those in Table 1 of ICD. Top column shows the SDR data file 5-digitally identified by year (YY) and day (DDD).

SDR Header Files

SDR Record Data

Table 2 of ICD, except for parameter which 50 indicates a check on the tail of each count in .XXX.. Definition for each parameter is illustrated in Table 2 and 4 of ICD. Top column shows the SDR data file 5-digitally identified by year (YY) and date (DDD).

SDR Record Files | Download Cumulative Recovery Log for all tapes

The Navy GEOSAT Mission: An Overview, Johns Hopkins APL Technical Digest, Vol. 8, No. 2, 1987.

The Navy GEOSAT Mission Radar Altimeter Satellite Program, in Monitoring Earth's Ocean, Land, and Atmosphere from Space, Vol. 97, 1985 AIAA, p. 440-463.

J.J. Jensen, F.R. Wooldridge, The Navy GEOSAT Mission: An Introduction; McConathy, D. R. and C. C. Kilgus, The Navy GEOSAT Mission: An Overview, and W. E. Frain, M. H. Barbagallo, R. J. Harvey, The Design and Operation of GEOSAT, all in Johns Hopkins APL Technical Digest, Vol. 8, No. 2, 1987.

R.F. Gasparovic, R.K. Raney, R.C. Beal, Ocean Remote Sensing Research and Applications at APL, Johns Hopkins APL Technical Digest, Vol. 20, No 4, 1999, p. 600-610.

NOAA Report, Vol. IV, No 10, November 1995, ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/journals/noaa_report/GC58N61995v4no10.pdf

D.C. McAdoo, K.M. Marks, Gravity fields of the Southern Ocean from Geosat data, Journal of Geophysical Research, Vol. 97, 1992, p. 3247-3260.

G.H. Born, J.L. Mitchell, G.A. Heyler, Geosat ERM-Mission Design, Journal of the Astronautical Sciences, Vol. 35, No 2, April 1987, p. 119-134.

W.H.F. Smith, D.T. Sandwell, Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings, Science, 277, 1997, p. 1956-1961.

F.M. Monaldo, Expected Differences Between Buoy and Radar Estimates of Wind Speed and Significant Wave Height and Their Implications on Buoy-Altimeter Comparisons, Journal of Geophysical Research, Vol. 93, 1988, p. 2285-2301.

L. Miller, R.E. Cheney, B.C. Douglas, Geosat Altimeter Observations of Kelvin Waves and the 1986-87 El Nino, Science, 239, 1988, p. 52-54.

D.B. Chelton, M.G. Schlax, D.L. Witter, J.G. Richman, Geosat altimeter observations of the sea surface circulation of the southern ocean, Journal of Geophysical Research, Vol. 95, 1990, pp. 17,887-17,903.

M.J. Gabor, J.C. Ries, A Systematic Approach to the Precision Orbit Determination of the GEOSAT Exact Repeat Mission Utilizing TRANET Doppler Data, Proceedings of the AAS/AIAA Space Flight Mechanics Meeting, Austin, TX, Feb. 12-15, 1996, Paper: AAS 96-166.

J.L. MacArthur, P.C. Marth, Jr., J.G. Wall, The GEOSAT Radar Altimeter, Johns Hopkins APL Technical Digest, Vol. 8, No. 2, April-June 1987.

D.R. Mantripp, J.K. Ridley, C.G. Rapley, Antarctic map from the Geosat Radar Altimeter Geodetic Mission, ESA Earth Observation Quarterly, No. 37-38, May-June 1992, p. 6-10.

GEOSAT-A Data Users/ground system interface control document (ICD). Johns Hopkins APL, May 1985.