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Description

Provides L1B low resolution (LR) short time critical (STC; 36-hour latency) altimetry data from the Poseidon-4 SAR altimeter on the Sentinel-6A Michael Freilich spacecraft which include the geolocated, fully-calibrated pulse-limited LR power echoes. The S6A STC product is analogous to the Jason-3 IGDR product.

Product Summary

Platforms
Sentinel-6A
Instruments
Poseidon-4 Radar Altimeter
Spatial Extent

N: 66.15 S: -66.15 E: 180 W: -180

Geographic Region
GLOBAL ,
GLOBAL OCEAN
Coordinate System
CARTESIAN
Granule Spatial Representation
GEODETIC
Temporal Extent
2020-12-07
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C1968980593-POCLOUD
Data State
ACTIVE
Number of Files/Granules
46671
Processing Level
1B
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

SENTINEL-6. (2021). Sentinel-6A MF/Jason-CS L1B P4 Altimeter Low Resolution (LR) STC Geolocated Waveforms [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/S6AP4-1BLST Date Accessed: 2025-12-14

Documents

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
/data_20/c/altimeter_clock This is the actual altimeter clock. The altimeter clock is based upon the USO clock. The nominal USO clock is 10MHz, while the nominal altimeter clock is 395 MHz. The actual USO clock is provided regularly as a drift information: based on the USO drift, the actual altimeter clock is computed, assuming a linear dependency. The USO clock closest in time is used. Hz int -2147483647 N/A 1.0E-6
/data_20/c/altimeter_power_drift This is a measure of the instrument power drift. It is mainly composed of a temperature-dependent harmonic variation along the orbit and a long-term decay. It is regularly measured from CAL1 impulse response with respect to a reference at the beginning of the mission. the instrument power drift closest in time is used. dB short -32767 N/A 0.01
/data_20/c/altitude Altitude of the satellite center of mass above the reference ellipsoid (WGS-84). m int -2147483647 N/A 0.0001
/data_20/c/altitude_rate Instantaneous altitude rate at the center of mass with respect to the reference ellipsoid (WGS-84) m/s int -2147483647 N/A 0.0001
/data_20/c/attenuation_calibrated The ISPs contain the ATT command applied within a radar cycle. The actual ATT value, which slightly differs from the nominal one, is extracted from a look-up table. The Attenuation closest in time is used. dB short -32767 N/A 0.01
/data_20/c/cal1_power Max or Total power of the instrument PTR from the CAL1 measurement. The choice of Max vs Total power is specified in the mcd_flags. Either case, the cal1_power waveform has been corrected for (a) calibrated attenuation correction, (b) variable digital gain and (c) residual cal1 fixed digital gain. dB short -32767 N/A 0.01
/data_20/c/hn_mean This field is for monitoring the H0/COR2 decoding into CAI (Coarse Altitude instruction) and FAI (Fine Altitude Instruction). In LRM it is the altitude instruction (CAI+FAI) averaged and rounded over the radar cycle. In SAR, it is the altitude instruction (CAI+FAI) averaged and rounded over the burst closest to the nadir of the surface location. NOTE: T0 = 1/altimeter_clock_ku. The mean altitude closest in time is used. T0/16/64 uint 4294967295 N/A 1
/data_20/c/l1b_record_counter The L1B record counter, starting from 0 for each product 1 int -2147483647 N/A 1
/data_20/c/latitude Latitude of measurement [-90, +90]. Positive latitude is North latitude, negative latitude is South latitude degrees_north int -2147483647 N/A 1.0E-6
/data_20/c/longitude Longitude of measurement [0, 360). East longitude relative to Greenwich meridian degrees_east int -2147483647 N/A 1.0E-6
/data_20/c/manoeuvre_flag Flags contained within the NAVATT file N/A byte -1 0 to 1 1
/data_20/c/mcd_flags set of error flags linked to the information retrieval common for LR and HR. When equal to 0 the information has been retrieved correctly. If equal to 1 an error has occurred when retrieving the information. N/A short -1 0 to 1023 1
/data_20/c/off_nadir_pitch_angle_pf Pitch angle with respect to the nadir pointing, measured by the STRs and post-processed by AOCS or by ground facility. The attribute ‘added_bias’ contains the estimated pitch bias. Note: nominal pointing is at satellite nadir (antenna perpendicular to ellipsoid) and corresponds to: pitch = 0 degrees int -2147483647 N/A 1.0E-7
/data_20/c/off_nadir_roll_angle_pf Roll angle with respect to the nadir pointing, measured by the STRs and post-processed by Attitude and Orbit Control System(AOCS) or by ground facility. The attribute ‘added_bias’ contains the estimated roll bias. Note: nominal pointing is at satellite nadir (antenna perpendicular to ellipsoid) and corresponds to: roll = 0 degrees int -2147483647 N/A 1.0E-7
/data_20/c/off_nadir_yaw_angle_pf Yaw angle with respect to the nadir pointing, measured by the STRs and post-processed by AOCS or by ground facility. The attribute ‘added_bias’ contains the estimated yaw bias. Note: nominal pointing is at satellite nadir (antenna perpendicular to ellipsoid) and corresponds to: yaw = 0 degrees int -2147483647 N/A 1.0E-7
/data_20/c/orbit_type_flag Orbit type used for the product generation N/A byte -1 0 to 8 1
/data_20/c/p4_instrument_configuration_flags It contains flags from ISPs related to P4 configuration and tracking. N/A byte -1 0 to 63 1
/data_20/c/p4_mode_flag Flag containing the mode identifier from the P4 instrument source packets N/A byte -1 5 to 19 1
/data_20/c/power_scaling_to_antenna The overall instrument gain, including: (a) attenuator_calibrated, (b) variable_digital_gain, (c) cal1_power_drift, (d) g_scaling, (e) antenna_gain. This variable is applied to the power waveform, and once it is applied the resulting L1B waveform is equivalent to the ratio of received vs transmitted power. dB short -32767 N/A 0.01
/data_20/c/power_waveform The L1B LR power waveform is a fully calibrated low resolution pulse limited waveform. It includes: (a)the power calibration given by the variable 'power_scaling_to_antenna' so that the waveform power is referenced at antenna flange, (b) configuration according to flag_processing_configuration, (c) final scaling, given in the variable 'waveform_sclae_facotr', in order to best fit waveform into 2 bytes 1 ushort 65535 N/A 1
/data_20/c/ptr_main_lobe_width Width of the CAL1 waveform main lobe at -3dB s int -2147483647 N/A 1.0E-12
/data_20/c/pulse_repetition_interval The Pulse Repetition Interval. PRI is constant within all received pulses in a radar cycle, but it can change within consecutive radar cycles. It is provided in counters of (T0*8) by the altimeter, with T0 = 1/altimeter_clock_ku. The PRI closest in time is used. s int -2147483647 N/A 1.0E-12
/data_20/c/range_cor_com It is the (1-way) distance in the z-component between the center of mass and the antenna reference point. The z-component closest in time is used. m short -32767 N/A 0.0001
/data_20/c/range_cor_doppler One-way Doppler range correction due to satellite altitude rate applied to calibrated tracker range. m short -32767 N/A 0.0001
/data_20/c/range_cor_internal_delay_att This is the 1-way range correction due to the delay introduced by the attenuator. m short -32767 N/A 0.0001
/data_20/c/range_cor_internal_delay_cal The internal path delay is periodically measured in flight with a dedicated CAL pulse per radar cycle, or by means CAL1 LR and HR sequences. The CAL1 closest in time is used. m short -32767 N/A 0.0001
/data_20/c/range_cor_reference_sample Poseidon 4 includes a 20480 samples IFFT on board. After the IFF there is a range selection block to allow for selecting a subset of these 20480 samples. This subset is then telemetered on ground. The first sample, and the width of the selected echo is configurable per measurement mode and available in telemetry. [N_FS-N_CS+samples]*T0 is the two-way correction, which multiplied by the speed of light and converted to one-way is equivalent to this variable. m short -32767 N/A 0.0001
/data_20/c/range_cor_uso It is the USO Drift (1-way) range correction. The USO drift is applied directly to the clock. This variable has been included for monitoring purpose. The USO Drift closest in time is used. m short -32767 N/A 1.0E-5
/data_20/c/sig0_scaling_factor The scaling factor in order to retrieve sigma-0 from L1B waveform. It includes the antenna gains and all the geometry factors satellite-surface, according to the radar equation. It is not applied to the l1b waveforms. It has to be applied to the re-tracked value of the (power_waveform*waveform_scale_factor) dB short -32767 N/A 0.01
/data_20/c/snr_instr_estimation instrument estimated SNR from Telemetry, converted from engineering to physical units. The SNR is estimated on tracking waveform (N-2). In the L1B HR it is the average of the snr_instr_estimation at 140Hz of all contributing Doppler beams within the stack. This value is only available for Ku band, for C band it should be set to _Fillvalue dB short -32767 N/A 0.01
/data_20/c/surface_classification_flag 7-state surface type classification from MODIS and GlobCover N/A byte -1 0 to 6 1
/data_20/c/telemetry_type_flag Telemetry packet type: LRM, RAW or RMC. A Level 1B product can include combinations of SAR RAW and RMC telemetry packets N/A byte -1 0 to 3 1
/data_20/c/time Time refers to the instant the L1B waveform (which is a combination of pulses for both LR and HR) touches the surface. [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 double N/A N/A 1
/data_20/c/time_tai Time refers to the instant the L1B waveform (which is a combination of pulses for both LR and HR) touches the surface. [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 double N/A N/A 1
/data_20/c/tm_cor2 The COR2 (altitude rate estimation) value, copied from ISP. The altimeter estimates one COR2 value per radar cycle. It is used in combination with the H0 to compute the CAI and FAI instructions. NOTE: T0 = 1/altimeter_clock_ku. The COR2 closest in time is used. T0/16/64 int -2147483647 N/A 1
/data_20/c/tm_h0 The H0 (initial altitude instruction) value, copied from ISP. The altimeter provides one H0 value per radar cycle. It is used in combination with the COR2 to compute the CAI and FAI instructions. NOTE: T0 = 1/altimeter_clock_ku. The closest H0 in time is used. T0/64 int -2147483647 N/A 1
/data_20/c/tm_source_sequence_counter This is the instrument record counter, copied from ISP. 1 short -32767 N/A 1
/data_20/c/tracker_range_calibrated This is the 1-way distance from the satellite's center of mass to the middle of the range window (sample ns/2 from 0). It includes the following range calibrations: (a) range_corr_internal_delay_cal, (b) range_corr_internal_delay_diff, (c) range_corr_external_group_delay, (d) range_corr_com. Note: the actual altimeter clock (variable 'altimeter_clock_ku') has been used to compute the altimeter range m int -2147483647 N/A 0.0001
/data_20/c/tracker_range_calibrated_diode This is the 1-way distance from the satellite's center of mass to the middle of the range window as given by the DIODE+DEM (sample ns/2 from 0). It includes the following range calibrations: (a) range_corr_internal_delay_cal, (b) range_corr_internal_delay_diff, (c) range_corr_external_group_delay, (d) range_corr_com. Note: the actual altimeter clock (variable 'altimeter_clock_ku') has been used to compute the altimeter range m int -2147483647 N/A 0.0001
/data_20/c/variable_digital_gain Variable component of the gain produced by the digital processing unit. The variable gain closest in time is used. dB short -32767 N/A 0.01
/data_20/c/velocity_vector velocity vector at the center of mass in ITRF. The 3 components are given according to the 'space_3d' dimension: [1] x, [2] y, [3] z m/s int -2147483647 N/A 0.0001
/data_20/ku/altimeter_clock This is the actual altimeter clock. The altimeter clock is based upon the USO clock. The nominal USO clock is 10MHz, while the nominal altimeter clock is 395 MHz. The actual USO clock is provided regularly as a drift information: based on the USO drift, the actual altimeter clock is computed, assuming a linear dependency. The USO clock closest in time is used. Hz int -2147483647 N/A 1.0E-6
/data_20/ku/altimeter_power_drift This is a measure of the instrument power drift. It is mainly composed of a temperature-dependent harmonic variation along the orbit and a long-term decay. It is regularly measured from CAL1 impulse response with respect to a reference at the beginning of the mission. the instrument power drift closest in time is used. dB short -32767 N/A 0.01
/data_20/ku/altitude Altitude of the satellite center of mass above the reference ellipsoid (WGS-84). m int -2147483647 N/A 0.0001
/data_20/ku/altitude_rate Instantaneous altitude rate at the center of mass with respect to the reference ellipsoid (WGS-84) m/s int -2147483647 N/A 0.0001
/data_20/ku/attenuation_calibrated The ISPs contain the ATT command applied within a radar cycle. The actual ATT value, which slightly differs from the nominal one, is extracted from a look-up table. The Attenuation closest in time is used. dB short -32767 N/A 0.01
/data_20/ku/cal1_power Max or Total power of the instrument PTR from the CAL1 measurement. The choice of Max vs Total power is specified in the mcd_flags. Either case, the cal1_power waveform has been corrected for (a) calibrated attenuation correction, (b) variable digital gain and (c) residual cal1 fixed digital gain. dB short -32767 N/A 0.01
/data_20/ku/hn_mean This field is for monitoring the H0/COR2 decoding into CAI (Coarse Altitude instruction) and FAI (Fine Altitude Instruction). In LRM it is the altitude instruction (CAI+FAI) averaged and rounded over the radar cycle. In SAR, it is the altitude instruction (CAI+FAI) averaged and rounded over the burst closest to the nadir of the surface location. NOTE: T0 = 1/altimeter_clock_ku. The mean altitude closest in time is used. T0/16/64 uint 4294967295 N/A 1
/data_20/ku/l1b_record_counter The L1B record counter, starting from 0 for each product 1 int -2147483647 N/A 1
/data_20/ku/latitude Latitude of measurement [-90, +90]. Positive latitude is North latitude, negative latitude is South latitude degrees_north int -2147483647 N/A 1.0E-6
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