Altimetry Data Archive


File Format Types of Files

Instructions


Data files may be in one of two formats:

File Format 1

Field Value Units
1 Point number Ordinal
2 Latitude Degrees
3 Longitude Degrees
4 Time Days Since 01Jan1985
5 Sea surface height anomaly Meters

File Format 2

The data is written to file by tracks. For each track within the file there is a header. For every good data point within that track there follows a record.

Header format Record format
Field Value
1 Track number
2 Cycle number
3 Number of good data points
Field Value Units
1 Track number Ordinal
2 Point number Ordinal
3 Latitude Degrees
4 Longitude Degrees
5 Calendar day See below
6 Time of day See below
7 Sea surface height anomaly Meters
8 Significant wave height Meters
9 Wind speed Meters/second

Calendar day format:yyyymmdd where yyyy = year, mm = month, and dd = day.

Time of day format:hhmmsscc where hh = hour, mm = minute, ss = second, and cc = hundredths of a second.


Types of files

The data files are of two types:

Daily files are created each day to include only the new data that was received and processed that day. For many of the altimeters raw data is first received with a quickly derived orbit and then an improved orbit set of data is received soon after. Separate daily files are maintained for each of these data sets. Each of these files generally contain one day of data, but may contain more or less depending on when the raw data files are received.

File name format: ppppyyyy_ddd

pppp = prefix

yyyy = year

ddd = julian day

Prefix Type Description
tpx1 TOPEX Initial orbit topex data
tpx2 TOPEX Final orbit topex data
ers2 ERS-2 ERS-2 data
gfoo GFO Doppler (initial) orbit GFO data
gfoM GFO Laser (final) orbit GFO data

Archive or permanenet files are created as the data becomes available. Each file contains 10 days of data. These files contain the best data available. It is assumed that the improved orbit data is better and generally comprises the data in these files.

File name format: ppp_yyyy_ddd_ddd

ppp = prefix

yyyy = year

ddd = julian day(first and last)

Prefix Type
tpx TOPEX
ers ERS-2
gfo GFO

Please note: All files are compressed and will have a .Z suffix

This page was last updated 21 December 2001.