Description of Sea Surface Height Data

• General Information
  • Brief Description
  • Procedure
  • Format
  • Dataset Naming Convention and Descriptions

• Satellite-Specific Information
  Version Updates and Information
  Edits and Flags
  • TOPEX/POSEIDON
    
    
  • ERS2
    
    
  • ERS1
    
    
  • GEOSAT
    
    

Files containing regularly spaced, spatially-indexed, colinear sea surface heights with respect to a reference mean sea surface are provided.

Altimeter satellites that are maintained in a repeating orbit facilitate the separation of sea height variations from the geoid. The term "colinear" indicates that sea surface heights for a particular "exact repeat orbit" mission have been georeferenced to a specific groundtrack. The colinear data file contains sea surface heights for each orbit cycle at fixed locations thus allowing for the direct computation of SSH ( Sea Surface Height ) variability .

The sea surface heights corrected for all geophysical, media, and instrument effects are given at 1 second intervals ( about 6 km ) along the reference track. In addition to the sea surface height file there are ancillary files that provide the georeferenced locations, the reference mean sea surface at the georeferenced locations, a quality control file that contains a flagword for each observation and a file that provides the observation time at index 1 for each revolution . Software to access all of the files are provided .

1. Compute improved Geophysical Data Records ( GDRs )
2. Obtain, analyze, and apply the latest state-of-the-art corrections and models, consistent across missions, whenever possible .
3. Spatially and temporally interpolate to reference groundtrack at 1/sec sampling
4. Apply editing criteria to extract bad data
5. Flag data based on quality control criteria

Alongtrack Index

Revolution Number

Array of Sea Surface Heights in mm

Summary Information of Altimeter Repeat Missions for Ocean Pathfinder Data Sets as of 7/18/2002

Satellite	No. of Days/Repeat Cycle	Revolutions/Repeat Cycle	Revolution Period in seconds	No. of Repeat Cycles	Span of Data
TOPEX/POSEIDON	9.92	127	6745	356	09/23/1992 - 05/24/2002
ERS2	35.00	501	6036	70	04/29/1995 - 11/19/2001
ERS1 ( Phase C )	35.00	501	6036	18	04/14/1992 - 12/20/1993
ERS1 ( Phase G )	35.00	501	6036	13	03/24/1995 - 06/02/1996
GEOSAT ( ERM )	17.05	244	6038	62	11/08/1986 - 09/30/1989
GFO	17.05	244	6038	45	01/07/2000 - 01/26/2002

ssh.dat

File containing the sea surface height residuals (mm) with along track index and revolution number

ssh_noib.dat

File containing the sea surface height residuals (mm) with along track index and revolution number
Sea surface heights DO NOT have the inverted barometer correction applied

reforb.dat

File containing geodetic North latitude and East longitude in microdegress of georeferenced locations

mss.dat

GSFC mean sea surface (GSFC00.1_MSS) interpolated to the indexed georeferenced locations (cm)

flagword.dat

Data quality flagword for each observation based on certain criteria.

time.dat

Observation time at index 1 for each revolution. All times are in terms of Modified Julian Dates.

directry.dat

Directory of direct-access record numbers referenced by revolution and alongtrack index .

Please note that a revolution is defined as the ground track between consecutive ascending equator crossings

The SSH array contains sea surface heights referenced to the GSFC00.1 mean sea surface (Wang, Y.M., "The satellite altimeter data derived mean sea surface GSFC98", GRL, Vol.27, No.5, p.701-704, March 1, 2000.)

Corrected SSH = SSH + (dr+dx*cos(lat)*cos(lon)+ dy*cos(lat)*sin(lon)+ dz*sin(lat))

lat = North latitude
lon = East longitude

These offsets were computed by solving for dr,dx,dy,dz from crossover residuals wrt a T/P 1993 mean profile for GEOSAT and coincident T/P mean profiles for ERS-1 and ERS-2. Note that for ERS-2 the range measurement on the CERSAT OPR had already been corrected for an estimated instrument bias of 40.9 cm.

• Equatorial Radius = 6378136.3 m
• Flattening = 1/298.257

TOPEX/ POSEIDON	ERS2	ERS1	GEOSAT