ASAR, MERIS and AATSR products

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1 ASAR, MERIS and AATSR products Francesco Sarti and Steffen Dransfeld ESA/ESRIN 25 February 2008

2 ENVISAT Launched in Sun-synchronous polar orbit (SSO): Nominal reference orbit of mean altitude 800 km, 35 days repeat cycle, 10:00 AM mean local solar time (MLST) descending node, deg. inclination. Dimensions: - Launch configuration: length 10.5m - In-Orbit Configuration: 26m x 10m x 5m Mass: - Total satellite 8140 Kg (including 319 Kg hydrazine) - Payload 2050 Kg Solar Array power: 6.5 kw (EOL) Average Power demand: Sun Eclipse (watts) (watts) Payload Satellite Launch vehicle: Ariane 5 (single launch)

3 Advanced Synthetic Aperture RADAR (ASAR) TECHNICAL CHARACTERISTICS: Sensor Type: Imaging microwave radars Accuracy: Radiometric resolution in range: db Spatial Resolution: Image, Wave and Alternating Polarisation modes: approx 30m x 30m.. Wide Swath mode: approx 150m x 150m.. Global Monitoring mode: approx 1000m x 1000m. Swath Width: Image and alternating polarisation modes: km (depending on incidence angle: degrees), Wave mode: 5km, Wide swath and global monitoring modes: 400km or more Waveband: Applications: Microwave: C-band, C with choice of 5 polarisation modes (VV, HH, VV/HH, HV/HH, or VH/VV) Ocean and Coast (Ocean Currents and Topography) Land (Landscape Topography) Snow and Ice (Snow and Ice)

4 About ASAR IM AP WS GM WV Image Mode 7 beams: deg. inc. angle VV or HH polarisation Swath width: 56 Km 106 Km Wide Swath & Global Monitoring Mode 5 ScanSAR beams VV or HH polarisation Swath width: ~ 400 Km Alternating Polarisation Mode 7 beams: deg. inc. angle VV/HH, VV/VH and HH/HV polarisation Swath width: 56 Km 106 Km Wave Mode 7 beams: deg. inc. angle + 2 alternate beams capability VV or HH polarisation 1 imagette every 100 Km

5 ASAR Image Mode Swaths ASAR provides dual-channel data: in Alternating Polarization Mode, it provides one of three different channel combinations: VV and HH HH and HV VV and VH Tx Rx Tx Rx

6 ASAR acquisition modes Asar Image mode (IM) VV or HH polarization images from any of 7 selectable swaths. Swath width between approximately 56 Km (swath 7) and 100 Km (swath 1) across-track. Spatial resolution of approximately 30m (for precision product) ASAR Alternating polarization mode (AP) Two co-registered images per acquisition, from any of 7 selectable swaths. HH/VV, HH/HV or VV/VH polarization pairs possible. Spatial resolution of approximately 30m (for precision products)

7 ASAR acquisition mode ASAR Wide Swath Mode (WS) 400 Km by 400 Km wide swath image. Spatial resolution of approximately 150m by 150m for nominal product. VV or HH polarization ASAR Global Monitoring Mode (GM) Spatial resolution of approximately 1Km in azimuth by 1Km in range for nominal product. Swath 400 Km Up to a full orbit of coverage, HH or VV polarization

8 ENVISAT Product Levels Data products Radar Imagery Envisat s data products are divided into three categories Level 0, 1 or 2 depending on the amount of processing needed to transform raw satellite data. Level 0: raw satellite data

9 Product Level 0 (raw satellite data)

10 Product Level 1 f1

11 Slide 10 f1 To be extended to the case of ALOS PalSAR. Remark: level 1.1 is phase-preserving (for polarimetric processing with POLSARPRO), level 1.5 is not fsarti, 03/03/2008

12 Product description For details see the ASAR Handbook available at

13 This ASAR WSM image is the first transmitted via the satellite ARTEMIS. Acquistion: 12-Mar-2003 The variation in grey tone within the Usangu wetlands indicates a spatial variability in soil moisture. As can be seen over the lakes, water is like a mirror for signal radar, reflecting specularly away from the antenna the energy backscattered. As a result, wet areas generate dark grey tones within the image.

14 Poyang Lake, China. 10 June 2007 Example of surface water mapping using Envisat ASAR WSM imagery. June 2007

15 This ASAR APP image shows an area covering the country of Guinea The image is a colour composite where: Red: HV polarised image Green: HH polarised image Blue: Ratio between the amplitude in HH and HV. The brown yellow colour that dominates the image results from the sparse vegetation (savannah) that covers the area (medium-low HV and HH backscattering, but HV backscattering higher than HH). The capital, Conakry is seen in cyan tones as it is densely populated (dominant HH backscattering). From the city of Conakry to northeast is seen a bright fringe in yellow colour due to the increasing of vegetation and human settlements (high HH and HV backscattering). Coastal plains of Guinea are plenty of swamps, seen in blue tones in the image corresponding to wet areas (low HH and HV backscattering and HV lower than HH)

16 Landers (USA) earthquake (1993) Bam (Iran) earthquake (26 Dec. 2003) Envisat ASAR Interferogram Visible fault Bam Blind fault revealed by ASAR ERS-1 SAR Interferogram 35 days apart

17 Techniques: SAR Interferometry (InSAR) Radar interferometry is based on the quantitative Acquisition at time 1 T R comparison (phase difference) between paired complex SAR images (taken at different times, ENVISAT/ERS, or simultaneously, SRTM) φi φf interferometric phase φ r - φ r = Δφ Acquisition at time 2 φi T R φf Interferogram of the Vajont landslide Δφ = Δφ DISP + Δφ TOPO + Δφ ATMO + Δφ NOISE Different techniques exist to separate the phase contribution due to ground displacements (case of non simultaneous acquisitions)

18 Techniques: SAR interferometry Tempo T 0 R 1 tempo T 0 +Δt R 1 = R 2 Δ r 1 acquisition 2 acquisition Laion Landslide Permits to assess ground deformations with centimetric accuracy Δφ = Δφ DISP + Δφ TOPO + Δφ ATMO + Δφ NOISE

19 Techniques: Differential interferometry (DInSAR) SAR Image (ERS) differential interferogram interferometric phase Detection of ground movements occurred in the time span between two acquisitions with an accuracy of a small fraction of wavelength Satellite: Acquisitions from different positions (baseline >0) Df = Df TOPO + Df MOV Ground-based: Acquisitions from the same position (baseline =0) Df = Df MOV

20 Techniques: Permanent Scatterers pixel by pixel analysis multi-image processing ESA - ERS Los Angeles Processing technique of SAR images which allows to assess deformations with millimetric accuracy on single specific points (PS), coincident with highly reflective elements on the ground surface 35 giorni 100 Km Dataset of SAR images 100 Km tempo

21 Overflowing Sliding inner slope Overtopping Plastic horizontal sliding BLUE Below Sea level km of water barriers: 3565 km primary water barriers (big rivers, sea, IJsselmeer, Markermeer), >14000 km regional water barriers Piping Nipping ice On the potential of PS-InSAR for monitoring dikes in the Netherlands Courtesy R. Hanssen Delft Institute of Earth Observation and Space Systems

22 ASAR Training Course, Hanoi, 25 February 7 March 2008 dike monitoring Landsat background, with PSI-dike results of 9 frames superposed ( ) On the potential of PS-InSAR for monitoring dikes in the Netherlands Courtesy Ramon Hanssen, Delft Institute of Earth Observation and Space Systems

23 More Information on ASAR Data ESA webpage containing general information about ASAR Envisat ASAR product handbook: ok.2_2.pdf Contains all information about different ASAR products, their formats, how they are generated, what they are used for, etc.

24 Medium Resolution Imaging Spectrometer (MERIS) TECHNICAL CHARACTERISTICS: Sensor Type: Spatial Resolution: Swath Width: Waveband: Applications: Imaging multispectral radiometer (vis( vis/nir) Ocean: 1040m x 1200 m, Land & coast: 260m x 300m 1150km, global coverage every 3 days VIS-NIR: 15 bands selectable across range: 390 nm to 1040 nm (bandwidth programmable between 2.5 and 30 nm) Ocean and Coast (Ocean Colour/Biology) Land (Vegetation) Atmosphere (Clouds, Precipitation)

25 Pushbroom Imager ( 5 cameras) Total swath width: 1150 Km Full Resolution: 300 m Reduced resolution: 1200 m About MERIS VIS-NIR Spectrometer within spectral range: 390 to 1040 Nanometers 15 bands electronically programmable (in width and position) 1150 km

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32 Processing levels available

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34 Level 1b (geolocated, calibrated TOA radiances) Structure Spectral bands: Radiance measurements at all 15 different wavelengths

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38 This MERIS FR image shows two huge sand dune seas in the Fezzan region of southwestern Libya. Image Acquired: 24 Nov Spatial Resolution: 300 m Swath Width 672 km A persistent high-pressure zone centred over Libya keeps the heart of the Sahara completely arid for years at a time, but research has discovered evidence of 'paleolakes' in this region associated with a wetter and more fertile past. Libya today has no permanent rivers or water bodies, but has various vast fossil aquifers. These natural underground basins hold enormous amounts of fresh water.

39 MERIS image showing phytoplankton upwelling, Mauritania Acquistion: 22-Mar- 2002

40 In this MERIS image the contrast can clearly be seen between the desert areas of Senegal in the north to the vegetated coastal plains of Guinea- Bissau, The Gambia and Southern Senegal (shown in red on the image). The green colour of the sea around the islands of the Buagos Archipelago is caused by sediment being swept out to sea from the river Acquistion: 24-Feb-2004

41 One of the first images acquired by Envisat, this MERIS image shows the complex river system inside Casamance with its heavy discharge into the sea. A series of such images are needed to monitor the transport of sediment which arises from inland soil erosion. This scene covers the transition zone between savannah in the north and tropical vegetation in the south. MERIS can also monitor the intensification of land use which leads to increased erosion and soil loss. Acquistion: 22-Mar-2002 Casamance, Senegal

42 Water Quality in Egypt MERIS-based relative water turbidity index MERIS-based relative water chlorophyll-a index 5 May May May May 2006 Examples of MERIS Derived Products

43 More Information on MERIS Data ESA webpage containing general information about MERIS Envisat MERIS product handbook: Contains all information about different MERIS products, their formats, how they are generated, what they are used for, etc.

44 MERIS images (not N1. products but full jpeg in the true colour bands) can be found on: Miravi: Earth Watching: Image Gallery (nice images taken from "image of the week"): Background Regional Mission (places where ENVISAT acquires images by default when there are no programming requests, e.g. major cities, areas prone to disaster - like active volcanoes, etc): (under construction, but hopefully soon ready!)

45 Advanced Along Track Scanning TECHNICAL CHARACTERISTICS: Radiometer (AATSR) Type Accuracy Spatial Resolution: Swath Width: Waveband: Applications: Imaging multi-spectral radiometers (vis( vis/ir) & Multiple direction / polarisation radiometers Sea surface temperature: <0.5K over 0.5 deg x 0.5 deg (lat/long) area with 80% cloud cover. Land surface temperature: 0.1K (relative) IR ocean channels: 1km x 1km, Visible land channels: 1km x 1km 500km VIS - NIR: : 0.555, 0.659, micrometers, SWIR: : 1.6 micrometers, MWIR: : 3.7 micrometers, TIR: : 10.85, 12 micrometers Ocean and Coast (Sea Surface Temperature),, Atmosphere (Atmospheric chemistry (Trace Gases, Clouds), Land (Vegetation)

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50 RGB combination of: Red = 870 micrometer reflectance channel Green = 670 micrometer reflectance channel Blue = 550 micrometer reflectance channel AATSR image over Caspian Sea

51 Lake surface temperature Derived from 3 AATSR scenes: 16-AUG AUG AUG-2006

52 More Information on AATSR Data ESA webpage containing general information about AATSR: Envisat AATSR product handbook: Contains all information about different AATSR products: their formats, how they are generated, what they are used for, etc.