An Overview of Synthetic Aperture Radar and Commercial Spaceborne SAR Systems GEOINT Symposium April 2014 Tom Ager Geomatics Consulting and Teaching TomAgerLLC An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter Clouds Don’t Matter Properly selected radar frequencies are not affected by the atmosphere Radar energy goes thru clouds, dust and volcanic ash Planet Ocean Other Useful Properties Day and Night Coverage Radar provides it own illumination High Resolution Synthetic Aperture Radar, SAR Flexible Resolution and Coverage Hi-res small areas, Mid-res medium areas, Low-res Large areas Outstanding Geometric Accuracy Precise measurements Traditional Images and Many other Products Enabled by coherent illumination The Electromagnetic Spectrum Microwave Band Wavelength (µm) P 133 cm Frequency (Hz) Television and Radio 108 106 S 106 108 C 104 1010 102 1012 Thermal Infrared L X K V Visible 1 W mm 0.1 cm 1014 10-2 1016 10-4 1018 10-6 1020 Microwave Reflected Infrared Ultraviolet (UV) X-Rays Gamma rays Cosmic rays An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter Radar as Echo Measurement System Backscatter Radar transmits a pulse then measures echo •  Radar antenna emits individual pulses of microwave radiation •  Pulse repetition frequency (PRF) is 2000 / second or more •  Radar measures characteristics of echoes •  Time, strength, “phase” of return wave •  Phase data are very valuable… •  Energy is “coherent”… the waves are in synch, like a laser Range and Azimuth Dimensions Range Spotlight Mode Small areas, best resolution Stripmap Mode Long, wide swaths of medium resolution Time Beamwidth •  Time of return… gives us range •  Strength of return… gives us brightness •  Phase of return… gives us magic Hill Shadow Trees River Strength Range direction Trees Hill Measuring the Echo Radar Angles Depression Angle Grazing Angle Incidence Angle Notice… Grazing and Incidence Angles are Complements Be careful when ordering… 300 Graze is 600 Incidence An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter Surface Effects on Reflectance Corner reflection Specular reflection Diffuse reflection Airborne SAR Washington, DC A mixture of Diffuse, Specular and Corner reflections Airborne SAR Lincoln Memorial Proper interpretation requires that you consider the geometry of collection Radar Shadow Resulting image line Reflected signal strength Radar Shadows are Completely Black They are null pixels… no data Radar Shadow Radar shadows are areas on the ground not illuminated by the radar because of viewing geometry and terrain relief Sandia National Labs, Ku-band SAR image Radar Foreshortening Objects are positioned on SAR images based on range. For a given line in the image, features that have the same range will occupy the same pixel. Notice that the front side of the mountain will be displayed in a few pixels. The front of the mountain will look compressed on the image. NASA SIR-C Mission Kamchatka, Russia Radar Layover The peak of the mountain has the same range as the flat area in front of it The mountain peak will “layover” towards that area Radar Layover Layover increases when the collection angle becomes steep… opposite optical! Layover direction is perpendicular to the flight path of the sensor Radar Image Layover © Infoterra GmbH / DLR Courtesy: Digital Globe The Alamo Dome San Antonio Texas Access road highlighted This is NOT a SAR Thing ! Foreshortening on Far Side of Oblique Image The geometry of SAR and optical are different… but both are subject to Foreshortening and Layover depending on the collection geometry Wanna See Some Layover ? Collect Off-Nadir with Optical For optical this is called “Relief Displacement” An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter We Are In Control Radar antennas emit coherent pulses of electromagnetic microwaves We pick the Wavelength and Frequency We pick the Orientation… or Polarization Vertical Polarization Electric Field Magnetic Field Horizontal Polarization Magnetic Field Electric Field RADARSAT2 Image C-Band HH This is a typical SAR image in which the transmitted and recorded polarizations are identical. This is sometimes called co-pol imaging. RADARSAT-2 Data and Products © MacDonald, Dettwiler and Associates Ltd. All Rights Reserved. RADARSAT is an official mark of the Canadian Space Agency. RADARSAT2 Image C-Band HV Notice the dramatic reflectance differences between this image and it co-polarized mate. When radar pulses are reflected from ground objects, the reflected wave does not always have the same polarization as the transmitted wave. The reflected polarization depends on the physical structure of ground objects. It possible to record the shifted polarization, thus creating a crosspolarized image (HV or VH). The cross-polarized options of HV and VH produce nearly identical images. RADARSAT-2 Data and Products © MacDonald, Dettwiler and Associates Ltd. All Rights Reserved. RADARSAT is an official mark of the Canadian Space Agency. RADARSAT2 Image C-Band VV Commercial space radars are now capable of polarized imaging. The are two basic modes: dual- and quadpolarization. Dual-pol systems produce some combination of two differently polarized images. Quad-pol systems produce four: HH, HV, VV, VH RADARSAT-2 Data and Products © MacDonald, Dettwiler and Associates Ltd. All Rights Reserved. RADARSAT is an official mark of the Canadian Space Agency. RADARSAT2 Multi-Pol Composite Red (HH), Green (HV), Blue (VV) Since HV and VH are identical, a quad-pol system like RADARSAT2 actually produces three unique images. In this example they are used to produce a false-color composite. Research is underway to help determine the composition of ground objects based on polarization signatures. RADARSAT-2 Data and Products © MacDonald, Dettwiler and Associates Ltd. All Rights Reserved. RADARSAT is an official mark of the Canadian Space Agency. An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter The Commercial SAR Space Systems RADARSAT2 TerraSAR-X TanDEM-X COSMO-SkyMed 1,2,3,4 MacDonald Dettwiler Astrium Services / Infoterra GmbH ASI / Telespazio / e-Geos 14 Dec 2007 15 July 2007 21 June 2010 8 Jun and 12 Dec 2007 25 Oct 08, 5 Nov 2010 C-Band X-Band X-Band Channel Polarization Quad Dual Dual Nominal Target Revisit Time at mid-latitudes 3 days 2.5 days 0.5 days (4 vehicles) Launch Dates Frequency Band Orbit Repeat Cycle Best Resolution Widest Swath 1, 3, 4 or 8 Days 24 Days 11 Days 0.8 m x 3 m 0.24m x 0.7 m 1m* 500 km 266 km 200 km Depending on Vehicle Combinations * Cosmo has the highest native range resolution, value includes multi-look processing to reduce noise Space-based SAR Collection Notice the geometry of collection… Long imaging period, side looking, long distance from ground area Notice Anything ? COSMO SkyMed ©ASI Processed and distributed by e-GEOS An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter The Cenepa War January thru February 1995 •  Military Conflict between Peru and Ecuador •  Fought over disputed border region in Cordillera Del Condor •  High, rugged, poorly mapped area in foothills of Andes •  Mediation Efforts Led to Peace Agreement •  Solved the longest territorial dispute in Western Hemisphere •  Mapped un-demarcated stretch of border, deep in Amazonian rainforest Disputed Border Region GEOINT Support to Mediators •  RADARSAT Large-Area Mosaic •  Elevation Data •  “Rapidscene” System •  Early version of interactive flythrough technology •  Unclassified, Sharable ComSAR Data •  Used by all members of mediation team •  Peru, Ecuador, Argentina, Brazil, Chile, United States •  Member nations were thrilled with imagery and technology provided by NIMA •  Mapping of negotiated border avoided WW III and Saved Civilization ! •  Other Imagery Option •  Go fly airplanes over this very rugged, elevated area •  And make sure they have SAR ! Extensive Hardcopy Mapping Coverage Interactive Flythrough System 3-D Hardcopy Anaglyph Unclassified, Shareable ComSAR Data Please Touch ! Disputed Border Region An Overview of Imaging Radar and Commercial Space Systems Why Radar Matters The Nature of Radar Illumination Radar Image Characteristics A Few Notes on Polarized Illumination The Commercial SAR Space Systems How ComSAR Saved Civilization Why Commercial SARs Matter Only Source of… Unclassified, Sharable Imagery with Fast Global Access Collection Through Clouds and Dust Good Resolution via SAR Flexible Resolution and Coverage Multiple Polarizations Outstanding Precision Images and other Derived Products Thank You Danke Grazie Tom Ager Geomatics Consulting and Teaching TomAgerLLC