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Description

These data are near-real-time (NRT) (within 7-9 hours of measurement) sea surface height anomalies (SSHA) from the AltiKa altimeter onboard the Satellite with ARgos and ALtiKa (SARAL). SARAL is a French(CNES)/Indian(SARAL) collaborative mission to measure sea surface height using the Ka-band AltiKa altimeter and was launched February 25, 2013. The major difference between these data and the Operational Geophysical Data Record (OGDR) data produced by the project is that the orbit from SARAL has been adjusted using SSHA differences with those from the OSTM/Jason-2 GPS-OGDR-SSHA product at inter-satellite crossover locations. This produces a more accurate NRT orbit altitude for SARAL with accuracy of 1.5 cm (RMS), taking advantage of the 1 cm (radial RMS) accuracy of the GPS-based orbit used for the OSTM/Jason-2 GPS-OGDR-SSHA product. This dataset also contains all data from the project (reduced) OGDR, and improved altimeter wind speeds and sea state bias correction. More information on the SARAL mission can be found at: http://www.aviso.oceanobs.com/en/missions/current-missions/saral.html

Product Summary

Platforms
SARAL
Instruments
ALTIKA Altimeter
Spatial Extent

N: 82 S: -82 E: 180 W: -180

Spatial Resolution
8000 Meters x 8000 Meters
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2020-03-18
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C2251465126-POCLOUD
Data State
ACTIVE
Number of Files/Granules
26155
Processing Level
2
Published
Updated
Science Keywords
Sea Surface Height ,
Significant Wave Height

Citation

Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.

Copy Citation

NASA/JPL. (2013). SARAL Near-Real-Time Value-added Operational Geophysical Data Record Sea Surface Height Anomaly [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/AKASA-XOGD1 Date Accessed: 2025-12-14

Documents

USER'S GUIDE

DATA CITATION GUIDELINES

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Variables

Variables are a set of physical properties whose values determine the characteristics or behavior of something. For example, temperature and pressure are variables of the atmosphere. Parameters and variables can be used interchangeably. Variable level attributes provide individual information for each variable.

The Name in this table is the variable name. Fill value indicates missing or undefined data points in a variable. Valid range is the range of values the variable can store. Scale factor is used to increase or decrease the size of an object and can be used to correct for distortion. For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor
alt Altitude of satellite above the reference ellipsoid. Associated quality flag is orb_state_flag_diode for the OGDR products, orb_state_flag_rest for the IGDR and GDR products m int 2147483647 N/A 0.0001
alt_dyn Altitude of satellite above reference ellipsoid, derived from dynamic fit to DORIS-DIODE orbit. m int 2147483647 N/A 0.0001
bathymetry ocean depth/land elevation m int 2147483647 N/A 1
ecmwf_meteo_map_avail Possible values are: 0 meaning '2 maps, nominal' (six hours apart), 1 meaning '2 maps, degraded' (more than six hours apart), 2 meaning '1 map, closest map used', 3 meaning 'no valid map' N/A byte 127 N/A 1
hf_fluctuations_corr Provided as a correction to the inverted barometer correction (inv_bar_corr) m short 32767 N/A 0.0001
ice_flag See SARAL User Handbook N/A byte 127 N/A 1
internal_tide See SARAL User Handbook m short 32767 N/A 0.0001
inv_bar_corr Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. See SARAL User Handbook m short 32767 N/A 0.0001
iono_corr_gim An ionospheric correction must be added (negative value) to the instrument range to correct this range measurement for ionospheric range delays of the radar pulse. See SARAL User Handbook m short 32767 N/A 0.0001
lat Positive latitude is North latitude, negative latitude is South latitude. See SARAL User Handbook. Associated quality flag is orb_state_flag_diode for the OGDR products, orb_state_flag_rest for the IGDR and GDR products degrees_north int N/A N/A 1.0E-6
lon East longitude relative to Greenwich meridian. See SARAL User Handbook. Associated quality flag is orb_state_flag_diode for the OGDR products, orb_state_flag_rest for the IGDR and GDR products degrees_east int N/A N/A 1.0E-6
mean_sea_surface_sol1 See SARAL User Handbook m int 2147483647 N/A 0.0001
mean_topography See SARAL User Handbook m int 2147483647 N/A 0.0001
model_dry_tropo_corr Computed at the altimeter time-tag from the interpolation of 2 meteorological fields that surround the altimeter time-tag. A dry tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for dry tropospheric range delays of the radar pulse. See SARAL User Handbook m short 32767 N/A 0.0001
ocean_tide_sol2 Includes the equilibrium long-period ocean tide height (ocean_tide_equil) and the short-period part of the corresponding loading tide (load_tide_sol2). The permanent tide (zero frequency) is not included in this parameter because it is included in the geoid and mean sea surface (geoid, mean_sea_surface_sol1). See SARAL User Handbook m int 2147483647 N/A 0.0001
pole_tide See SARAL User Handbook m short 32767 N/A 0.0001
rad_liquid_water Should not be used over land kg/m^2 short 32767 N/A 0.01
rad_surf_type Set to 1 = land if the K-band (first channel) radiometer land fraction is greater than a given threshold N/A byte 127 N/A 1
rad_water_vapor Should not be used over land kg/m^2 short 32767 N/A 0.1
rad_wet_tropo_corr Computed at the altimeter time-tag from the radiometer brightness temperatures, the Ka-band backscatter coefficient, the sea surface temperature and the lapse rate (decreasing rate of the atmosphere temperature with altitude). A wet tropospheric correction must be added (negative value) to the instrument range to correct this range measurement for wet tropospheric range delays of the radar pulse m short 32767 N/A 0.0001
range All instrumental corrections included, i.e. distance antenna-COG (cog_corr), USO drift correction (uso_corr), internal path correction (internal_path_delay_corr), Doppler correction (doppler_corr), modeled instrumental errors correction (modeled_instr_corr_range) and system bias m int 2147483647 N/A 0.0001
sea_state_bias A sea state bias correction must be added (negative value) to the instrument range to correct this range measurement for sea state delays of the radar pulse. This element should not be used over land. See SARAL User Handbook m short 32767 N/A 0.0001
sig0 All instrumental corrections included, excepted the system bias, i.e. AGC instrumental errors correction, internal calibration correction (internal_corr_sig0), modeled instrumental errors correction (modeled_instr_corr_sig0) and atmospheric attenuation (atmos_corr_sig0) dB short 32767 N/A 0.01
solid_earth_tide Calculated using Cartwright and Tayler tables and consisting of the second and third degree constituents. The permanent tide (zero frequency) is not included. See SARAL User Handbook m short 32767 N/A 0.0001
ssha = altitude of satellite (alt) - corrected altimeter range (range) - gim ionospheric correction (iono_corr_gim) - model dry tropospheric correction (model_dry_tropo_corr) - radiometer wet tropospheric correction (rad_wet_tropo_corr) - sea state bias correction (sea_state_bias) - solid earth tide height (solid_earth_tide) - geocentric ocean tide height solution 2 (ocean_tide_sol2) - geocentric pole tide height (pole_tide) - inverted barometer height correction (inv_bar_corr) - high frequency fluctuations of the sea surface topography (hf_fluctuations_corr) - mean sea surface solution 1 (mean_sea_surface_sol1). Calculated even if iono_corr_gim or hf_fluctuations_corr are at default value m short 32767 N/A 0.001
ssha_dyn = sea surface height anomaly (ssha) - DIODE altitude of satellite (alt) + Dynamic fit to DIODE altitude of satellite (alt_dyn) - sea surface height cross over correction (xover_corr). The only difference with ssha is that ssha_dyn uses the orbit altitude from alt_dyn instead of alt and applies the cross over correction xover_corr. Note that by applying the cross over correction this sea surface height is implicitly leveled to Jason-2/OSTM sea surface height observations. m short 32767 N/A 0.001
surface_type Computed using a DTM2000 file: 0 = open oceans or semi-enclosed seas; 1 = enclosed seas or lakes; 2 = continental ice; 3 = land. See SARAL User Handbook N/A byte 127 N/A 1
swh All instrumental corrections included, i.e. modeled instrumental errors correction (modeled_instr_corr_swh) and system bias m short 32767 N/A 0.001
time [tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. [leap_second] is the UTC time at which a leap second occurs in the data set, if any. After this UTC time, the [tai_utc_difference] is increased by 1 second seconds since 2000-01-01 00:00:00.0 double N/A N/A 1
trailing_edge_variation_flag See SARAL User Handbook N/A byte 127 N/A 1
wind_speed_alt Should not be used over land. See SARAL User Handbook. A calibration bias of -0.21 dB has been added to the backscatter coefficient (sig0) before computing the wind speed m/s short 32767 N/A 0.01
xover_corr Calculated using a fit of a bias and 1 cycle per revolution sinusoid to crossovers of sea surface height anomalies between SARAL (using alt_dyn) and Jason-2/OSTM. m short 32767 N/A 0.0001
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