The U.S. 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
- Ship tapes (20–40 per week)
- Recover data in tapes, save to DVDs and send DVDs back to NCEI
- Check received DVDs and back up
- Check data recovery quality
- Verify the tape recovery checklist and obtain approval of tape disposal from NCEI
- Archive the recovered data
Tape Damage Details
Geosat SDR Recovery Table Graphic
- 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.
- 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
- The lost number of records count during the data recovery because of tape damage
- The frame count of the data record is before the beginning frame count indicated in the header
- The data are after the ending frame count in the header
- The frame count in a data record was before the previous record's frame count
- The frame count jumped by more than 1199, which is a 2-minute gap (1200/10 = 120 seconds = 2 minutes)
- 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
About Data Range Checks
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
- Data value is within the data range
- Data value is out of the lower bound
- 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 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).
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