Lesson 1, Topic 1
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Sentinel-1 data access

How can I obtain free radar data?

Within the framework of the Copernicus Programme of the European Commission, Sentinel data is freely accessible to anyone.

As we have learned, the Sentinel family includes two radar satellite constellation Sentinel-1A & -1B, operating at C-Band. In this topic you will learn how to obtain the data, which imaging modes are available and which product level will best suit to your desired application.

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Sentinel-1 Image modes

Information on the different imaging modes of Sentinel-1, according to the Sentinel-1 Acquisition mode documentation.

Sentinel-1 image acquisition modes

Stripmap (SM)

(80 km Swath width | 5 by 5 m resolution)

Stripmap mode acquires data with an 80 km swath at 5 m by 5 m spatial resolution (single look). The ground swath is illuminated by a continuous sequence of pulses while the antenna beam is pointing to a fixed azimuth angle and an approximately fixed off-nadir angle. SM images have continuous along track image quality at an approximately constant incidence angle.

Polarisation modes

  • Dual (HH+HV, VV+VH)
  • Single (HH, VV)
TOPSAR technique as used in Sentinel-1’s IW mode

Interferometric Wide Swath (IW)

(250 km Swath width | 5 by 20 m resolution)

The Interferometric Wide swath mode is the main acquisition mode over land and satisfies the majority of service requirements. It acquires data with a 250 km swath at 5 m by 20 m spatial resolution (single look).

Azimuth resolution is reduced compared to SM due to the shorter target illumination time of the burst. IW mode captures three sub-swaths using Terrain Observation with Progressive Scans SAR (TOPSAR). Bursts are synchronised from pass to pass to ensure the alignment of interferometric pairs.

With the TOPSAR technique, in addition to steering the beam in range as in ScanSAR, the beam is also electronically steered from backward to forward in the azimuth direction for each burst, avoiding scalloping and resulting in homogeneous image quality throughout the swath.

Polarisation modes

  • Dual (HH+HV, VV+VH)
  • Single (HH, VV)

Extra Wide Swath (EW)

(400 km Swath width | 20 by 40 m resolution)

Similar to the IW mode, the Extra Wide swath mode employs the TOPSAR technique to acquire data over a much wider area using five sub-swaths. EW mode acquires data over a 400 km swath at 20 m by 40 m spatial resolution.

EW SLC products contain one image per sub-swath and one per polarisation channel, for a total of five (single polarisation) or 10 (dual polarisation) images in an EW product.

The EW mode is aimed primarily for use over sea-ice, polar zones and certain maritime areas, in particular for ice, oil spill monitoring and security services. Like IW, EW mode can also be used for interferometry since it shares the same characteristics for burst synchronisation, baseline and Doppler stability.

Polarisation modes

  • Dual (HH+HV, VV+VH)
  • Single (HH, VV)

Wave Mode (WV)

(20 km Swath width | 5 by 5 m resolution)

Wave mode acquires data in 20 km by 20 km vignettes, at 5 m by 5 m spatial resolution, every 100 km along the orbit, acquired alternately on two different incidence angles. Vignettes on the same incidence angle are separated by 200 km.

SENTINEL-1 Wave mode is similar to ERS and ENVISAT wave mode imaging but with improved resolution, larger vignettes and a new ‘leap frog’ acquisition pattern. WV acquisitions consist of several vignettes exclusively in either VV or HH polarisation, with each vignette processed as a separate image. WV mode products can contain any number of vignettes, potentially amounting to an entire data-take. Each vignette will be contained in an independent image within the product.

Polarisation modes

  • Single (HH, VV)
Sentinel-1’s Alternating WV Mode Acquisitions

Excursion: Sentinel-1 Product levels

Radar images are available at different processing levels. That means that a certain amount of pre-processing has already been conducted by the data provider in each product level. It is important to know which processing steps have been done at each level before ordering the data. For many users it is advantageous to order high processing levels to reduce the effort of working with the data. For others, especially scientific users, it is desirable to order data as close to the RAW data as possible to enable customized processing.

If you are interested in learning about the Sentinel-1 processing levels, click the ‘Show More’ button and discover the product levels of Sentinel-1, as described by the Sentinel-1 Product level documentation.

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Sentinel-1 processing levels
Overview of the Sentinel-1 processing levels.
Inlcuded | Not included

Level 0

The SAR Level-0 products consist of compressed and unfocused SAR raw data. Level-0 products are the basis from which all other high level products are produced. For the data to be usable, it will need to be decompressed and processed using focusing software.

Level-0 data includes noise, internal calibration and echo source packets as well as orbit and attitude information.

Level-0 products are stored in the long term archives. They can be processed to generate any type of product during the mission lifetime and for 25 years after the end of the space segment operations.

Level-0 products are available to data users for only the SM, IW and EW modes.

Level 1

Level-1 focused data are the generally available products intended for most data users. The Level-0 product is transformed into a Level-1 product by the application of algorithms and calibration data to form a baseline engineering product from which higher levels are derived.

The processing involved to produce Level-1 data products includes pre-processing, Doppler centroid estimation, single look complex focusing, and image and post-processing for generation of the SLC and GRD products as well as mode specific processing for assembling of multi-swath products.

Level-1 products can be either Single Look Complex (SLC) or Ground Range Detected (GRD). Each acquisition mode can potentially generate Level-1 SLC and GRD products. GRD resolutions will depend on the mode and the level of multi-looking.

Level-1 Processing Flow

Single Look Complex

Level-1 Single Look Complex (SLC) products consist of focused SAR data, geo-referenced using orbit and attitude data from the satellite, and provided in slant-range geometry. Slant range is the natural radar range observation coordinate, defined as the line-of-sight from the radar to each reflecting object. The products are in zero-Doppler orientation where each row of pixels represents points along a line perpendicular to the sub-satellite track.

The products include a single look in each dimension using the full available signal bandwidth and complex samples (real and imaginary) preserving the phase information. The products have been geo-referenced using the orbit and altitude data from the satellite and have been corrected for azimuth bi-static delay, elevation antenna pattern and range spreading loss.

Ground Range Detected

Level-1 Ground Range Detected (GRD) products consist of focused SAR data that has been detected, multi-looked and projected to ground range using an Earth ellipsoid model such as WGS84. The ellipsoid projection of the GRD products is corrected using the terrain height specified in the product general annotation. The terrain height used varies in azimuth but is constant in range.

Ground range coordinates are the slant range coordinates projected onto the ellipsoid of the Earth. Pixel values represent detected magnitude. Phase information is lost. The resulting product has approximately square resolution pixels and square pixel spacing with reduced speckle at a cost of reduced geometric resolution.

Level 2

Level-2 consists of geolocated geophysical products derived from Level-1. Level-2 Ocean (OCN) products for wind, wave and currents applications may contain the following geophysical components derived from the SAR data:

  • Ocean Wind field (OWI)
  • Ocean Swell spectra (OSW)
  • Surface Radial Velocity (RVL).

The availability of components depends on the acquisition mode. The metadata referring to OWI are derived from an internally processed GRD product, the metadata referring to RVL (and OSW, for SM and WV mode) are derived from an internally processed SLC product.

OSW Spectra (image courtesy of CLS SOPRANO)

The OSW is generated from Stripmap and Wave modes only and is not available from the TOPSAR IW and EW modes. For Stripmap mode, there are multiple spectra derived from the Level-1 SLC image. For Wave mode, there is one spectrum per vignette.

Wind Speed Plot (image courtesy of CLS SOPRANO)

The OWI component is a ground range gridded estimate of the surface wind speed and direction at 10 m above the surface, derived from SM, IW or EW modes.

Surface Radial Velocity (image courtesy of CLS SOPRANO)

The RVL surface radial velocity component is a ground range gridded difference between the measured Level-2 Doppler grid and the Level-1 calculated geometrical Doppler. The RVL component provides continuity of the ASAR Doppler grid.

(Free) Radar Data Sources

The following list gives you an overview where to obtain free and commercial radar data from various institutions.

Earth Explorer

U.S. Geological Service

The Earth Explorer is a service provided by the USGS. It holds a vast archive of Earth observation data. Amongst several optical data sets and Digital Elevation Models, the following radar sensors and products can be found:

  • SIR-C
  • SRTM
VISIT EARTH EXPLORER

Vertex

Alaska Space Facility

Possibly one of the world’s largest repository for Earth observation data. The data portal of the Alaska Space Facility offers access to the following radar data sets:

  • Sentinel-1
  • NASA UAVSAR
  • ALOS PALSAR
  • Radarsat-1
  • ERS-1/-2
  • JERS-1
  • AIRSAR
  • SeaSat
VISIT ASF VERTEX

JPL UAVSAR

Jet Propulsion Laboratory

NASA JPL provides access to its Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data.

  • NASA UAVSAR
VISIT JPL UAVSAR

Rocket

Mashup

The web portal Rocket provides the opportunity to download data from all the Sentinels as well as other sensors. In terms of radar data, Rocket provides:

  • Sentinel-1
VISIT ROCKET

ALOS PALSAR Mosaic

Japanese Aerospace Exploration Agency

JAXA provides access to global mosaics of ALOS PALSAR as well as forest/non-forest maps derived from this data.

VISIT JAXA

TerraSAR-X

Airbus Defence & Space

The company Airbus, which developed TerraSAR- and TanDEM-X in collaboration with the German Aerospace Center, provides a data archive where data can be searched and ordered.

  • TerraSAR-X
VISIT AIRBUS

G-Portal

Japanese Aerospace Exploration Agency

JAXA provides another data portal where radar data can be searched and ordered.

  • JERS-1
  • ALOS-1
  • ALOS-2
VISIT G-PORTAL

CODE-DE

German Aerospace Center

The Copernicus Data and Exploitation Platform – Deutschland (CODE-DE) is the German entry point to the Sentinel Satellite Systems, their data products and the products of the Copernicus Services.

VISIT CODE DE

EO Browser

Sinergise

The EO browser is a tool to search, process and visualise Sentinel data, including Sentinel-1. It is very useful to produce maps quickly and easily.

VISIT EO BROWSER

Even more Data Sources

Here is a very comprehensive list of data mirrors and tools for Sentinel images.

krstn.eu – Awesome Sentinel

Data Access

Data Hubs and National Mirrors

Official datahubs and mirrors by the Copernicus partners and Collaborative Ground Segment members.

Partial Mirrors

Innitiatives to integrate specific Sentinel data into existing search and discovery platforms.

Cloud Providers

Providers that host Copernicus Sentinel data and allow you to bring your own code to process it.

Tools

Specific to Copernicus Sentinel data discovery, download and processing.

Search & Download

Viewers & Browsers

Processing

## Products Products, datasets and applications generated from Copernicus Sentinel data.

krstn.eu – Awesome Sentinel

(Free) Radar Data Sources

The following list gives you an overview where to obtain free and commercial radar data from various institutions.

Earth Explorer

U.S. Geological Service

The Earth Explorer is a service provided by the USGS. It holds a vast archive of Earth observation data. Amongst several optical data sets and Digital Elevation Models, the following radar sensors and products can be found:

  • SIR-C
  • SRTM
VISIT EARTH EXPLORER

Vertex

Alaska Space Facility

Possibly one of the world’s largest repository for Earth observation data. The data portal of the Alaska Space Facility offers access to the following radar data sets:

  • Sentinel-1
  • NASA UAVSAR
  • ALOS PALSAR
  • Radarsat-1
  • ERS-1/-2
  • JERS-1
  • AIRSAR
  • SeaSat
VISIT ASF VERTEX

JPL UAVSAR

Jet Propulsion Laboratory

NASA JPL provides access to its Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data.

  • NASA UAVSAR
VISIT JPL UAVSAR

Rocket

Mashup

The web portal Rocket provides the opportunity to download data from all the Sentinels as well as other sensors. In terms of radar data, Rocket provides:

  • Sentinel-1
VISIT ROCKET

ALOS PALSAR Mosaic

Japanese Aerospace Exploration Agency

JAXA provides access to global mosaics of ALOS PALSAR as well as forest/non-forest maps derived from this data.

VISIT JAXA

TerraSAR-X

Airbus Defence & Space

The company Airbus, which developed TerraSAR- and TanDEM-X in collaboration with the German Aerospace Center, provides a data archive where data can be searched and ordered.

  • TerraSAR-X
VISIT AIRBUS

G-Portal

Japanese Aerospace Exploration Agency

JAXA provides another data portal where radar data can be searched and ordered.

  • JERS-1
  • ALOS-1
  • ALOS-2
VISIT G-PORTAL

CODE-DE

German Aerospace Center

The Copernicus Data and Exploitation Platform – Deutschland (CODE-DE) is the German entry point to the Sentinel Satellite Systems, their data products and the products of the Copernicus Services.

VISIT CODE DE

EO Browser

Sinergise

The EO browser is a tool to search, process and visualise Sentinel data, including Sentinel-1. It is very useful to produce maps quickly and easily.

VISIT EO BROWSER

Even more Data Sources

Here is a very comprehensive list of data mirrors and tools for Sentinel images.

krstn.eu – Awesome Sentinel

Data Access

Data Hubs and National Mirrors

Official datahubs and mirrors by the Copernicus partners and Collaborative Ground Segment members.

Partial Mirrors

Innitiatives to integrate specific Sentinel data into existing search and discovery platforms.

Cloud Providers

Providers that host Copernicus Sentinel data and allow you to bring your own code to process it.

Tools

Specific to Copernicus Sentinel data discovery, download and processing.

Search & Download

Viewers & Browsers

Processing

## Products Products, datasets and applications generated from Copernicus Sentinel data.

krstn.eu – Awesome Sentinel

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