Time Tags, Locations and Surface Types – Sentinel-3 Altimetry Technical Guide

Table 1: The distance to the coast is computed using the theoretical distance to the shore table of the Sentinel-3 mission.
Table 2: The orbit parameters (latitude and longitude) are computed, interpolating them at the time of the measurement.
Table 3: The time-tags of the measurements are the UTC seconds elapsed since 1 January 2000.
Table 4: The altitude rate of the altimeter measurement is used to determine the closest grid point to the shore table.
Table 5: The altitude is computed, interpolating it at the time of measurement.
Table 6: The surface type can be set to open ocean or semi-enclosed seas, enclosed seas or lakes, continental ice or land.

Table 1. Distance to the coast
PARAMETER	Distance to the coast
NETCDF NAME	dist_coast_[x1]_[x2] where: [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	Distance to the coast at time time_[x1]_[x2]. The distance to the coast is computed using the theoretical distance to the shore table of the Sentinel-3 mission. The altitude rate of the altimeter measurement is used to determine the closes grid point to the shore table.
UNITS	m
DATA SET AVAILABILITY	Reduced: 1 Hz only Standard: 20 Hz Ku-band only Enhanced: 20 Hz Ku-band only
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands: GEN_ENV_DIS_01 20 Hz Ku-band: GEN_ENV_DIS_01 20 Hz C-band: none
ADDITIONAL INFORMATION	None
PARAMETERS RELATED	None
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

Table 2. Latitude and Longitude
PARAMETER	Latitude and Longitude
NETCDF NAME	lat_[x1]_[x2] lon_[x1]_[x2] [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	Latitude position at time time_[x1]_[x2]. Longitude position at time time_[x1]_[x2]. This algorithm uses an ESA library called CFI Software Explorer Orbit that computes both latitude and longitude, interpolating them from the satellite orbit state vector positions file at the precise time of the input measurement.
UNITS	10^-6 degrees
DATA SET AVAILABILITY	Reduced: 1 Hz only Standard: all Enhanced: all
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands: Orbit CFI algorithm 20 Hz Ku-band: Orbit CFI algorithm 20 Hz C-band: Orbit CFI algorithm
ADDITIONAL INFORMATION	Positive latitude is North latitude, negative latitude is South latitude. East longitude relative to the Greenwich meridian.
PARAMETERS RELATED	None
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

Table 3. Time tags
PARAMETER	Time-Tag
NETCDF NAME	time_[x1]_[x2] where: [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	Time of the occurrence of the measurement. UTC time elapsed since January 1^st 2000. This time has been: converted from on-board time counters referenced to the overflown surface referenced to the middle of the tracking cycle
UNITS	seconds
DATA SET AVAILABILITY	seconds
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands: ALT_MAN_TIM_01 algorithm 20 Hz Ku-band: SRAL Level-1B product 20 Hz C-band: SRAL Level-1B product
ADDITIONAL INFORMATION	None
PARAMETERS RELATED	UTC days and seconds in the day elapsed since January 1st 2000 (UTC_day_[x1]_[x2] and UTC_sec_[x1]_[x2]) Time-tag of the 1 Hz measurement (UTC_time_1hz_[x1]_[x2])
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

Table 4. Orbit
PARAMETER	Orbital Altitude Rate
NETCDF NAME	orb_alt_rate_[x1]_[x2] [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	The satellite altitude rate is the height rate of the satellite at time time_[x1]_[x2]. The reference surface for the orbital altitude rate is the combined mean sea surface/geoid surface. The orbital altitude rate is used to compute the Doppler correction on the altimeter range. This algorithm uses an ESA library called CFI Software Explorer Orbit that computes altitude rate interpolating it from the satellite orbit state vector positions file at the precise time of the input measurement.
UNITS	10^-2 m/s
DATA SET AVAILABILITY	Reduced: none Standard: all Enhanced: all
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands: Orbit CFI algorithm 20 Hz Ku-band: Orbit CFI algorithm 20 Hz C-band: Orbit CFI algorithm
ADDITIONAL INFORMATION	None
PARAMETERS RELATED	None
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

Table 5. Altitude
PARAMETER	Orbit altitude
NETCDF NAME	alt_[x1]_[x2] [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	The satellite altitude is the height of the satellite above the reference ellipsoid at time time_[x1]_[x2]. This algorithm uses an ESA library called CFI Software Explorer Orbit that computes altitude interpolating them from the satellite orbit state vector positions file at the precise time of the input measurement.
UNITS	10^-4 m. An offset of 700,000m to be added to the value read from the netCDF file.
DATA SET AVAILABILITY	Reduced: 1 Hz only Standard: all Enhanced: all
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands:Orbit CFI algorithm 20 Hz Ku-band: Orbit CFI algorithm 20 Hz C-band: Orbit CFI algorithm
ADDITIONAL INFORMATION	For further information about orbit CFI, CFI Website
PARAMETERS RELATED	None
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

Table 6. Surface type
PARAMETER	Surface types
NETCDF NAME	surf_type_[x1]_[x2] where: [x1]: 1 Hz or 20 Hz data rates [x2]: Ku-band or C-band
DESCRIPTION	Surface type at time time_[x1]_[x2]. Surface type is computed using the land/sea mask of the Sentinel-3 mission. The latitude and longitude of the altimeter measurement are used to determine the nearest grid point in the land/sea mask file. The surface type is set to the surface type reported for this nearest grid point.
UNITS	The possible surface types are: open ocean or semi-enclosed seas (0b) enclosed seas or lakes (1b) continental ice (2b) land (3b)
DATA SET AVAILABILITY	Reduced: 1 Hz only Standard: 1 Hz only Enhanced: 1 Hz only
OPERATING MODE AVAILABILITY	LRM and SAR
DATA ORIGIN	1 Hz Ku/C-bands: SRAL Level-1B product 20 Hz-Ku-band: SRAL Level-1B product 20 Hz C-band: SRAL Level-1B product
ADDITIONAL INFORMATION	None
PARAMETERS RELATED	Radiometer-derived surface type (rad_surf_type[x1]_[x2]): The algorithm that computes the radiometer-derived surface type is RAD_MAN_INT_03. This algorithm averages/interpolates the radiometer data at 7 Hz to the 1 Hz altimeter time tags.
PARAMETER DETAILED DESCRIPTION	ESA's Global Land and Ocean Mission for GMES Operational Services

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