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Description

Provides L1B high resolution (HR) 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 SAR processed and calibrated multi-looked HR Ku-band waveforms. 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
C1968979588-POCLOUD
Data State
ACTIVE
Number of Files/Granules
46123
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 High Resolution (HR) STC Geolocated Waveforms [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/S6AP4-1BHST 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/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/doppler_angle_start Doppler angle of the first contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/doppler_angle_stop Doppler angle of the last contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/gaussian_fitting_center_look position of the center of the Gaussian that fits the integrated power of the looks within a stack, with respect to look angle rad short -32767 N/A 1.0E-6
/data_20/ku/gaussian_fitting_center_pointing position of the center of the Gaussian that fits the integrated power of the looks within a stack, with respect to pointing angle rad short -32767 N/A 1.0E-6
/data_20/ku/gaussian_fitting_kurtosis Kurtosis of the Gaussian that fits the integrated power of the looks within a stack. Kurtosis is a measure of peakiness 1 short -32767 N/A 0.01
/data_20/ku/gaussian_fitting_skewness Skewness of the Gaussian that fits the integrated power of the looks within a stack. The skewness indicates how symmetric or asymmetric the power within the stack is 1 short -32767 N/A 0.01
/data_20/ku/gaussian_fitting_std Standard deviation of the Gaussian that fits the integrated power of the looks within a stack. It is given with respect to the look angle. The width at -3dB of this Gaussian can be retrieved the following way: width_3db = 2*sqrt(2*ln2)*gaussian_fitting_std rad short -32767 N/A 1.0E-6
/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/hr_mcd_flags set of error flags linked to the information retrieval only applicable to 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 byte -1 0 to 7 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
/data_20/ku/longitude Longitude of measurement [0, 360). East longitude relative to Greenwich meridian degrees_east int -2147483647 N/A 1.0E-6
/data_20/ku/look_angle_start Look angle of the first contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/look_angle_stop Look angle of the last contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/manoeuvre_flag Flags contained within the NAVATT file N/A byte -1 0 to 1 1
/data_20/ku/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/ku/num_looks_multilooking The number of looks that have been actually used within the multi-looking. The number of non-zero looks after stack-masking 1 short -32767 N/A 1
/data_20/ku/num_looks_start_stop The number of looks within the stack between start and stop angle. Some of these looks may be set entirely to zero (according to stack_mask_start_stop and excluded from the multilooking 1 short -32767 N/A 1
/data_20/ku/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/ku/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/ku/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/ku/orbit_type_flag Orbit type used for the product generation N/A byte -1 0 to 8 1
/data_20/ku/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/ku/p4_mode_flag Flag containing the mode identifier from the P4 instrument source packets N/A byte -1 5 to 19 1
/data_20/ku/pnr_estimation Peak to Noise Ratio estimation done on L1A burst-averaged waveform as: peak / noise_level, where noise_level is estimated from the first n (configurable) samples dB short -32767 N/A 0.01
/data_20/ku/pointing_angle_start Pointing angle of the first contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/pointing_angle_stop Pointing angle of the last contributing (non-zero) look to the L1B waveform rad short -32767 N/A 1.0E-6
/data_20/ku/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/ku/power_waveform The L1B HR oversampled power waveform is a fully calibrated high resolution multi-looked waveform. It includes: (a) all calibrations, which have been applied at L1A, (b) configuration according to flags_processing_configuration_ku and flag_hr_processing_configuration_ku, (c) final scaling, given in the variable 'waveform_scale_factor', in order to best fit the waveform into 2 bytes 1 ushort 65535 N/A 1
/data_20/ku/ptr_main_lobe_width Width of the CAL1 waveform main lobe at -3dB s int -2147483647 N/A 1.0E-12
/data_20/ku/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/ku/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/ku/range_cor_doppler One-way Doppler range correction due to satellite altitude rate effectively compensated during delay/Doppler processing. m short -32767 N/A 0.0001
/data_20/ku/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/ku/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/ku/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/ku/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/ku/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/ku/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/ku/stack_mask_start_stop The zero-mask applied to the stack before multilooking. Each element of the mask refers to a look in the stack and indicates the index of the first sample set to zero. The first num_looks_start_stop elements of the mask are valid, while the remaining ones are filled with 0 1 ubyte N/A N/A 2
/data_20/ku/surface_classification_flag 7-state surface type classification from MODIS and GlobCover N/A byte -1 0 to 6 1
/data_20/ku/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/ku/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/ku/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
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