GEOS 657 - Lecture 10

Home , Paz (satellite), SAOCOM, Seasat

GEOS 657 – MICROWAVE REMOTE SENSING SPRING 2019

Lecturer: F.J. Meyer, Geophysical Institute, University of Alaska Fairbanks; [email protected]

Lecture 10: SAR Image Acquisition Modes; Past, Current, & Future SAR Sensors; Basics of InSAR

Image: DLR, CC-BY 3.0

UAF Class GEOS 657

AVAILABLE SAR SENSORS

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Current and Future SAR Satellites

TerraSAR-X & TanDEM-X PAZ SAR

X-band Cosmo-SkyMed 1st and 2nd generation

ERS-1/2 Envisat Sentinel

RADARSAT-2 RCM

C-band RADARSAT-1

JERS-1 ALOS-1 ALOS-2

SAOCOM L-band Seasat

NISAR

BIOMASS P-band

1978 1990 2000 2010 Present Day Future

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Current and Future SAR Satellites Accessible Through ASF

TerraSAR-X & TanDEM-X PAZ SAR

X-band Cosmo-SkyMed 1st and 2nd generation

ERS-1/2 Envisat Sentinel-1

RADARSAT-1 RADARSAT-2 RCM C-band

JERS-1 ALOS-1 ALOS-2

SAOCOM L-band Seasat

NISAR

BIOMASS P-band

1978 1990 2000 2010 Present Day Future

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Resolution vs. Spatial Coverage

• Medium (10m-class) resolution large-coverage systems: – Sensors: Current: ALOS-2; Sentinel-1; RADARSAT-2 Most of the medium-res Future: SAOCOM; NISAR; RCM; BIOMASS data are free or low cost (not ALOS-2 and R-2) – These sensors are suitable for applications such as: • Monitoring medium to large scale surface deformation (e.g., subsidence; slopes) • Assessing impacts of hazards (flooding; earthquakes) • General mapping and change detection

• High (1m-class) limited-coverage resolution systems: – Sensors: Current: TerraSAR-X; TanDEM-X; COSMO-SkyMed constellation nd Future: PAZ SAR; COSMO-SkyMed 2 Gen High-res data is typically – These sensors are suitable for applications such as: more expensive • Mapping and analysis of urbanized environments (buildings, bridges) • Detecting localized hazards (sinkholes; small landslides) • As most high-res systems have higher repeat frequency  tracking of things that change quickly

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Free of Charge vs. Commercial

• Free of charge data: – Current: Sentinel-1 – Future: SAOCOM (partly); NISAR; BIOMASS; RCM

• Commercial data: – Current: TerraSAR-X; TanDEM-X; COSMO-SkyMed Constellation – Future: COSMO-SkyMed 2nd Gen; PAZ SAR

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MEANS OF DATA ACCESS (1) THE ALASKA SATELLITE FACILITY (ASF)

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A Short Intro to the Alaska Satellite Facility (ASF)

• ASF is NASA Distributed Active Archive Center (DAAC) for SAR Data – Established in 1991 as the prime U.S. downlink and processing center for SAR data – Operates three antennas for command uplink and data downlink of a series of NASA and non-NASA remote sensing satellite systems

• Currently, ASF is housing about 7PB of SAR data in its archives  all data available on spinning disks for immediate download

Visit ASF @ www.asf.alaska.edu

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Recent ASF Milestones

MAY 2015: ASF’S ALOS PALSAR DATA HOLDINGS BECOME UNRESTRICTED

MAY 2015: CORRECTED FOR GEOMETRIC AND RADIOMETRIC DISTORTIONS & RELEASE OF PALSAR RTC DATA AVAILABLE AS FULLY GEOCODED GEOTIFF

DEC 2015: ASF PROVIDES ACCESS TO GLOBAL SENTINEL-1A ARCHIVE

SPRING 2016: SELECTED AS DATA CENTER FOR UPCOMING NASA-ISRO SAR (NISAR) MISSION

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VERTEX – ASF’s Search and Download Interface https://vertex.daac.asf.alaska.edu/#

• Let’s look at the Vertex Search Engine in more detail:

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MEANS OF DATA ACCESS (2) THE EUROPEAN SPACE AGENCY

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All of ESA’s SAR data ESA’s Past and Current SAR Sensors are freely available

ERS-1 & -2 (European State Envisat ASAR (European Sentinel-1 A/B (European Agency ESA) State Agency ESA) State Agency ESA)

• Sentinel-1A: Since 2014 • Identical twin satellites • Sentinel-1B: Since 2016 • ERS-1: 1991 – 3/2000 • Same orbit as ERS-1/2 • 흀: 5.6cm (C-band) • ERS-2: 1995 – 7/2011 • Lifetime: 2002 – 8/2012 • Stripmap, TOPS Mode • 흀: 5.6cm (C-band) • 흀: 5.6cm (C-band) • Resolution: 5m – 100m • Stripmap mode only • Stripmap, ScanSAR • Swath: 80 - 400km • Resolution: ~ 25m • Resolution: 25m – 150m • 12 days repeat cycle (6 • Swath: 100km • Swath: 100 - 400km days in the constellation) • 35 day repeat cycle • 35 day repeat cycle • Polarization: HH, VV, • 1996-2000: tandem phase • Polarization: HH, HV, HH/HV, VV/VH (acquisitions 1 day apart) VV/HH, HH/HV, VV/HV • Some Level-2 ocean • Polarization: VV products Franz J Meyer, UAF GEOS 657: Microwave RS - 1212

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ESA’s Copernicus Space Program Holistic Earth Observation with a Multi-Sensor Constellation

S1A/B: Radar Mission Launched in ‘14 & ‘16

S2A/B: High Resolution Optical Mission S2A launched in ‘16

S3A/B: Medium Resolution Imaging and Altimetry Mission

S4A/B: Geostationary Atmospheric Chemistry Mission

S5P: Low Earth Orbit Atmospheric Chemistry Precursor Mission

S5A/B/C: Low Earth Orbit Atmospheric Chemistry Mission

Jason-CS A/B: Altimetry Mission

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ESA’s Science Hub Search and Download Interface https://scihub.copernicus.eu/dhus/#/home

• Let’s look at the SciHub interface:

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SAR IMAGE ACQUISITION MODES

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Different SAR Modes for different Applications Mode 1: Stripmap Mode SAR

• Stripmap Mode Observation radar Geometry: – Radar images a strip-like swath V parallel to satellite orbit H – Standard operational mode

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Different SAR Modes for different Applications Mode 1: Stripmap Mode SAR

• Stripmap Mode Observation radar Geometry: – Radar images a strip-like swath V parallel to satellite orbit H – Standard operational mode

• Properties: – Range resolution 100% dependent on transmitted bandwidth 푊 – Azimuth resolution defined by length of synthetic aperture which is defined by length of physical antenna

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Different SAR Modes for different Applications Mode 2: Spotlight Mode SAR

• To increase azimuth resolution, synthetic aperture length is increased by beam steering to selected area

• Non-continuous imaging (areas before and after the selected area cannot be imaged!)

• Properties: – Range resolution 100% dependent on transmitted bandwidth 푊 – Azimuth resolution defined by length of synthetic aperture which is now independent of length of physical antenna area to be imaged

Summary: higher resolution at the expense of spatial coverage

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Different SAR Modes for different Applications Mode 3: ScanSAR Mode

• To achieve wider swaths, synthetic aperture is divided into short pieces (bursts)

Length of Synthetic Aperture per burst 퐿  successive illumination of several parallel swaths for increased swath width (100 to 500km) • Properties: – Range resolution 100% dependent on transmitted bandwidth 푊 – Azimuth resolution defined by length of synthetic aperture dedicated to one #1 sub-swath (퐿) (shorter than 퐿, #2 hence, lower resolution than stripmap #3 mode)

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Examples of SAR Image Acquisition Modes

• Available Image Modes:

– ScanSAR Mode: • Lowest resolution – largest coverage

– Stripmap Mode (standard mode) • Intermediate resolution

– Spotlight Mode • Highest resolution – limited coverage

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Coverage of Standard Beam and ScanSAR

• Comparison of RADARSAT SWB and RADARSAT ST-6

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First Envisat/ASAR ScanSAR Image – Antarctic Peninsula

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Recently Developed SAR Modes Toward Full Resolution and Wide Swath SARs Terrain Observation by Progressive Scan (TOPS) Scan on Receive SAR (SweepSAR)

Scan beam forward in azimuth during burst

• Time-share synthetic aperture among elevation • Time-share pulse returns on receive with beams to increase swath multiple receive beams to increase swath • Scan beam forward in azimuth within burst to • Track receive echoes as they propagate improve radiometry across the swath • Degraded azimuth resolution • Narrow receive beam controls ambiguities

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THE SENTINEL-1 AND NISAR SENSORS

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Sentine-1: First SAR Sensor with Operational Character

• Sentinel-1 (2014 - 2021): First SAR satellite system with operational mission – Regular reliable observation according to operational requirements – Imaging all landmasses, coastal zones and shipping routes every six days – Specifically designed for InSAR

ASF’s Sentinel-1 SAR Archive

• Rapidly growing global S-1A archive  multitude of new SAR users / applications (complex) images SLC Sentinel-1 SAR Archive

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ASF’s Sentinel-1 SAR Archive

• Rapidly growing global S-1A archive  multitude of new SAR users / applications (only amplitude) images (only amplitude) GRD Sentinel-1 Sentinel-1 SAR Archive

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9 GEOS 657 - Lecture 10

NISAR: NASA L-/S-Band SAR for Global Deformation Mapping

Jet Propulsion Laboratory California Institute of Technology

NISAR (2020): • Full global coverage with every cycle • Rapid commanding & rapid data delivery for hazard monitoring • Specifically designed for InSAR

The Science of NISAR

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Some System Parameters

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NISAR Observation Concept

• Science targets are observed in specific fixed modes, with culling at high latitudes to reduce overlapped data takes, as explained on next slide

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NISAR’s Mode-Specific Science Targets in Observation Plan

Planned Acquisitions Background Land

Land Ice Background Land satisfies most Solid Earth Sea Ice and Ecosystems objectives Urban (small targets) US Agriculture Himalayas

India Agriculture • Each colored region represents a single radar mode chosen to satisfy multiple India Coastal Ocean science objectives over that area Sea Ice Type • Avoids mode contention that would interrupt time series

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What’s Next?

• Next lecture we will talk about the concepts of polarimetric SAR (PolSAR) and how PolSAR data can be used automatically classify the image into different scattering types.

• There is a fairly lengthy chapter in Woodhouse (2006) stretching from page 65 – 91. Reading this chapter is not a requirement but recommended for students that want to dive into PolSAR a bit more.

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