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... > Instruments > Earth Remote Sensing Instruments > Active Remote Sensing > Altimeters > Radar Altimeters > SWIM

Preferred term

SWIM  

Definition

  • SWIM is a new CNES Ku-band radar instrument, manufactured by TAS (Thales Alenia Space), Toulouse, France; it is based on the technology of a spaceborne radar altimeter. SWIM is the first ever space radar concept that is mainly dedicated to the measurement of ocean waves directional spectra and surface wind velocities through multi-azimuth and multi-incidence observations. Orbiting on a 519 km sun-synchronous orbit, its multiple Ku-band (13.575 GHz) beams illuminating from nadir to 10º incidence and scanning the whole azimuth angles (0-360º) provide with a 180 km wide swath and a quasi global coverage of the planet between the latitudes of ±80º. Scientific requirements for wave measurements: The main objective of SWIM is to provide directional wave spectra. The products delivered to users shall reach the following accuracies: • Nadir measurements: - Accuracy on SWH (Significant Wave Height) better than 10% or 50 cm (maximum) - Accuracy on wind speed about ± 2 m/s or 10% (whichever is the larger). • Wave spectrum measurements (beams 6°, 8°, 10°): - Resolution cell of 70 x 90 km2 for wave spectra - Observable wavelengths of waves in (70 m, 500 m) with an accuracy from 10% to 20% - Azimuth resolution in wave propagation direction : 15° - Accuracy in wave spectrum level : 15% within the half wave energy bandwidth with respect to the peak. • Backscattering coefficient measurements: - Absolute accuracy of ±1dB, relative accuracy between beams ±0.1dB. Such a wide range of observations, requiring high-range resolution (about 20 m on the ground), have led to design an instrument whose architecture and technology goes beyond what has been done on altimeter and scatterometer implementations. The global coverage and the reduction of telemetry budgets have required performing onboard range compression. The variety of signals at different incidences, the impact of the complex moving geometry of observation and the required real-time signal processing have led to propose onboard complete digital range compression on backscattered 320 MHz bandwidth signals. The design of the onboard compression and processing resulted from a trade-off between the instrument high level performances required, the needed correction for geometrical effects such as range migrations and performance of the acquisition and tracking loops. The multi-azimuth multi-incidence observations requirements have led to design an ambitious antenna subsystem that rotates at 5.6 rpm while transmitting six high power RF signals towards tunable directions. This configuration allows a 180 km wide swath and a quasi global coverage of the planet between the latitudes of ±80º. • Real aperture radar SWIM instrument - Ku-band (320 MHz bandwidth) - On-board digital processing - 6 distinct beams between nadir and 10° incidence (0°, 2°, 4°, 6°, 8° and 10°) - Rotating antenna at 5.6 complete rotations/min. (en)

Broader concept

Change note

  • 2019-12-19 09:00:49.0 [mmorahan] Insert Concept add broader relation (SWIN [1c7fb7a4-cedd-4328-b785-5b0774cf1990,559569] - Radar Altimeters [92ddaaca-40b2-4936-bc1a-28cc5743e8b8,544943]);
  • 2019-12-19 09:04:21.0 [mmorahan] insert AltLabel (id: null category: primary text: Surface Waves Investigation and Monitoring instrument language code: en); insert Definition (id: null text: SWIM is a new CNES Ku-band radar instrument, manufactured by TAS (Thales Alenia Space), Toulouse, France; it is based on the technology of a spaceborne radar altimeter. SWIM is the first ever space radar concept that is mainly dedicated to the measurement of ocean waves directional spectra and surface wind velocities through multi-azimuth and multi-incidence observations. Orbiting on a 519 km sun-synchronous orbit, its multiple Ku-band (13.575 GHz) beams illuminating from nadir to 10º incidence and scanning the whole azimuth angles (0-360º) provide with a 180 km wide swath and a quasi global coverage of the planet between the latitudes of ±80º. Scientific requirements for wave measurements: The main objective of SWIM is to provide directional wave spectra. The products delivered to users shall reach the following accuracies: • Nadir measurements: - Accuracy on SWH (Significant Wave Height) better than 10% or 50 cm (maximum) - Accuracy on wind speed about ± 2 m/s or 10% (whichever is the larger). • Wave spectrum measurements (beams 6°, 8°, 10°): - Resolution cell of 70 x 90 km2 for wave spectra - Observable wavelengths of waves in (70 m, 500 m) with an accuracy from 10% to 20% - Azimuth resolution in wave propagation direction : 15° - Accuracy in wave spectrum level : 15% within the half wave energy bandwidth with respect to the peak. • Backscattering coefficient measurements: - Absolute accuracy of ±1dB, relative accuracy between beams ±0.1dB. Such a wide range of observations, requiring high-range resolution (about 20 m on the ground), have led to design an instrument whose architecture and technology goes beyond what has been done on altimeter and scatterometer implementations. The global coverage and the reduction of telemetry budgets have required performing onboard range compression. The variety of signals at different incidences, the impact of the complex moving geometry of observation and the required real-time signal processing have led to propose onboard complete digital range compression on backscattered 320 MHz bandwidth signals. The design of the onboard compression and processing resulted from a trade-off between the instrument high level performances required, the needed correction for geometrical effects such as range migrations and performance of the acquisition and tracking loops. The multi-azimuth multi-incidence observations requirements have led to design an ambitious antenna subsystem that rotates at 5.6 rpm while transmitting six high power RF signals towards tunable directions. This configuration allows a 180 km wide swath and a quasi global coverage of the planet between the latitudes of ±80º. • Real aperture radar SWIM instrument - Ku-band (320 MHz bandwidth) - On-board digital processing - 6 distinct beams between nadir and 10° incidence (0°, 2°, 4°, 6°, 8° and 10°) - Rotating antenna at 5.6 complete rotations/min. language code: en);
  • 2019-12-19 09:37:44.0 [mmorahan] insert WeightedRelation (id: null related concept uuid: 7c3fab1c-d17e-4e5c-870e-994793c2594e relationship type: null relationship value: null generated by: null);
  • 2019-12-19 12:08:09.0 [mmorahan] Rename Concept update PrefLabel (SWIM);

URI

https://gcmd.earthdata.nasa.gov/kms/concept/1c7fb7a4-cedd-4328-b785-5b0774cf1990

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