MI4079~1.PPT

Canada Centre for Remote Sensing, Natural Resources Canada DATA ACQUISITION STRATEGIES Natural Resources Ressources naturelles Canada Canada To select a RADAR image for specific applications, the user has to be:  Radar-Smart: be knowledgeable about the sensor to be used;  Geo-smart: knowledge of t...

Canada Centre for Remote Sensing, Natural Resources Canada DATA ACQUISITION STRATEGIES Natural Resources Ressources naturelles Canada Canada To select a RADAR image for specific applications, the user has to be:  Radar-Smart: be knowledgeable about the sensor to be used;  Geo-smart: knowledge of the environmental criteria to be considered; Spaceborne Microwave Sensors have fixed characteristics e.g incident angle, frequency, polarization etc, so the most important criteria is the geo-smart criteria where the area, topography, land use and land cover and season need to be included in the information required for data acquisition. For sensors with multiple characteristics like RADARSAT, the Radar-Smart criteria is important given the variety of options involved, which are based on swath width, ground resolution, incident angle, and to a lesser extent, orbit and look direction. Depending on the application of interest, users have the ability to tailor the acquisition of RADARSAT data based on:  area of coverage and resolution;  viewing geometry or incident angle  look direction of the sensor  acquisition time (dusk or dawn)  levels of detail (pixel size)  positional accuracy with respect to a defined map projection  turnaround time from data acquisition to delivery  acquisition strategy (single/multiple data acquisition)  land use/land cover and topography Applications that involve dynamic phenomenon e.g. flooding, ground surface characteristics need to be considered due to the sensitivity of backscatter to changes in moisture content or ability to distinguish between land and water. Commonly considered are:  topography  basin morphology that control the extent of the flood  flow of water  the river width with respect to image resolution  the duration of the flood (flash flood, multi day events or multi-week events)  Broad cover types (forest cover, bare surfaces)  environmental conditions (snow/no snow, wind/no wind) This type of application requires near real time delivery of images. For this, the most suitable incident angle is small incident angle because it increases the contrast between land and water; Images can be acquired before the flood, during the flood to monitor evolution and regression of the flood, and after the flood for flood damage assessment. Applications which do not consider dynamic factors e.g. geological mapping, the geographic and environmental conditions to be considered in product selection/acquisition strategies include  size of area  size of the target of interest (resolution)  topography (range of elevation, aspect and slope inclination)  preferential lineament orientation (look direction)  surface cover (vegetated/bare)  time of acquisition (year, season and day) The incident angle should be steep and timing is not a priority. The Ordering Process: A number of steps are involved here: a) planning: This should take place, at least, 4 weeks before the acquisition and should be based on the geographical characteristics of the surface (topography, land cover, environmental conditions) and applications (land cover mapping, flood monitoring, coastal erosion monitoring, oil seep detection etc), which prescribe sensor configuration; b) order: should take place, at least, 2 weeks between the acquisition date c) satellite programming d) image acquisition: image is acquired and downlinked to an available participating ground station or stored on one the RADARSAT’s onboard tape recorders e) processing f) delivery (CD-ROM etc) Order Handling Graphical preparation of data requests – “Swath Planner” software and look direction User-selectable – Mode, beam, polarization – Reception facility – Processing facility More responsive to user requests Canada Centre for Remote Sensing, Natural Resources Canada The Ordering Process: A number of steps are involved here: a) planning: This should take place, at least, 4 weeks before the acquisition and should be based on the geographical characteristics of the surface (topography, land cover, environmental conditions) and applications (land cover mapping, flood monitoring, coastal erosion monitoring, oil seep detection etc), which prescribe sensor configuration; b) order: should take place, at least, 2 weeks between the acquisition date c) satellite programming (uploading of incident angle, and duration of acquisition) d) image acquisition: image is acquired and downlinked to an available participating ground station or stored on one the RADARSAT’s onboard tape recorders e) processing f) delivery (CD-ROM etc) https://www.nrcan.gc.ca/earth-sciences/geomatics/satellite -imagery-and-air-photos/satellite-imagery-and-products/ed ucational-resources/tutorial-satellite-data-reception/trackin g-the-satellites/9633 The Processing Journey: a) Mission Control System (MCS): receives user requests via order desk, sends image production requests to the processing facility, receives the image production reports etc b) Transmission of Acquired Data: data acquired is transmitted either in real time or stored on the onboard tape recorder for latter transmission; c) Archiving: non-urgent data are transferred to the archiving facility and stored while near-real request are sent electronically via data transfer network; d) Processing: Products are generated after signal data is received by the processing facilities. Data is processed using geometric and radiometric calibration, scaling and the products generated; e) Distribution: Products are delivered to the user either on digital media (CD-ROM) or via electronic means (for direct users). The products consists of SAR image or signal data on CD-ROM, etc and a processing report; Canada Centre for Remote Sensing, Natural Resources Canada Image Quality and Calibration Natural Resources Ressources naturelles CanadaCanada Image Quality and Calibration -Outlineo,  o, and  o (beta, gamma and sigma)  ◆ How do they differ? ◆ How to get these from DN (Digital Number) on product? o Digital Numbers on the Products and  ◆ Look Up Tables - Why? - Types RADARSAT Image Calibration ◆ Processor Functionality - Antenna Pattern Correction Canada Centre for Remote Sensing, Natural Resources Canada o, o, o and RADARSAT Data Image Creation: Downlinked signal data is converted to an image which is either left RAW (signal data product) or calibrated radiometrically and geometrically; and fully adjusted to ensure optimal use of the 8-bit and 16-bit dynamic range. Backscatter o per unit area in slant range o per unit area in ground range o per unit area of the incident wavefront (perpendicular to slant range) ,  , and RADARSAT Data Source: R.K. Raney, 1998 N.B. Geometry Approximations Canada Centre for Remote Sensing, Natural Resources Canada o,  o , and RADARSAT Data  10 * log sin   and  10 * log tan     0 jk 0 jk j 10 0 where j jk 0 jk 10 = range sample k = azimuth sample  j = incident angle  jk = RADAR BACKSCATTER COEFFICIENT ([dB] o jk o ◆ = RADAR BRIGHTNESS ([dB] Most natural radiometric observable of a RADAR - ◆ “backscatter per unit area in slant range” Requires no knowledge of local incident angle jk = GAMMA ([dB]) Canada Centre for Remote Sensing, Natural Resources Canada j ,  , and RADARSAT Data (Cont’d) Incident angle ( j ) ◆ should be local incident angle ◆ often use model geoid at sea level to define  j - approximate - may be significant radiometric approximation - may lead to significant error in backscatter coefficient Canada Centre for Remote Sensing, Natural Resources Canada Radiometric Calibration Ensures temporal and spatial stability and repeatability of radar backscatter measurement, Dependent on imaging system and processor Account for imaging and processing parameters of system and microwave propagation Calculations performed during the processing Relative and absolute calibration: RC describes the sensor’s ability to provide stable, repeatable measurements over periods of time, depends primarily on the electrical stability of the radar sensor. This is necessary for applications that require the use of multiple images; AC this relates pixels to specific radar backscatter and is useful for relating radar backscatter to a geophysical parameter e.g. soil moisture. Reference targets are used for calibration e.g. transponders that are set to known radar backscattering or passive corner reflectors with known radar backscatter and geographic areas of known backscatter previously measured. This is performed at regular intervals; Canada Centre for Remote Sensing, Natural Resources Canada Data Products Natural Resources Ressources naturelles Canada Canada Data Products -Outline- Radar Product Characteristics Signal Data, Single Look Complex, Georeferenced, Geocoded. Media Choices CD-ROM, Data Cartridge (8mm), CCT, Hardcopy. CEOS Standard File Format Spaceborne SARs RADARSAT-1 and -2 Canada Centre for Remote Sensing, Natural Resources Canada Introduction The purpose of this section is to introduce and explain the processing levels of generic radar products and their formats. For the current radar satellites the generic radar products are very similar in their characteristics, but have different names and acronyms. The different product names are explained in this section, but all cited examples are for RADARSAT-1 products. Canada Centre for Remote Sensing, Natural Resources Canada Classes of Radar Product Signal Data Georeferenced Products ◆ complex, detected, slant and ground range. Geocoded Products ◆ detected, ground range. Canada Centre for Remote Sensing, Natural Resources Canada Signal Data Raw radar echo data in in-phase and quadrature (I/Q) format In slant range Stripped of telemetry format information reassembled into contiguous radar range lines Not an image, must be processed using a SAR processor to an image product Canada Centre for Remote Sensing, Natural Resources Canada Georeferenced vs Geocoded Products Georeferenced products: ◆ relative geographic location is incorporated in the image. ◆ not corrected to a map projection and should not be used for mapping purposes. Geocoded products: ◆ geometrically corrected to conform to a map projection. ◆ often use ground control points and DEM to increase the geocoding accuracy. ◆ geocoded products are usually resampled to a standard square pixel size. See Table 3.1 for an overview of RADARSAT products Canada Centre for Remote Sensing, Natural Resources Canada Table 3.1 RADARSAT Product Characteristics Product Name RSI Name Format Single Look Complex (SLC) Single Look Complex Slant Range Georeferenced Fine Resolution (SGF) Path image Ground Range Georeferenced Extra-Fine Resolution (SGX) Path Image Plus Ground Range Systematically Geocoded (SSG) Map Image Ground Range Precision Geocoded (SPG) Precision Map Image Ground Range Mode Standard Fine Wide Extended High Extended Low Standard Fine Wide Extended High Extended Low ScanSAR Narrow ScanSAR Wide Standard Fine Wide Extended High Extended Low Standard Fine Wide Extended High Extended Low Same as Map Image Pixel Spacing Approx. (m) 11.6 x 5.1 4.6 x 5.1 11.6 x 5.1 11.6 x 5.1 8.1 x 5.1 12.5 x 12.5 6.25 x 6.25 12.5 x 12.5 12.5 x 12.5 12.5 x 12.5 25 x 25 50 x 50 8x8 3.125 x 3.125 10 x 10 8x8 10 x 10 12.5 x 12.5 6.25 x 6.25 12.5 x 12.5 12.5 x 12.5 12.5 x 12.5 Same as Map Image # Looks 1x1 1x1 1x1 1x1 1x1 1x4 1x1 1x4 1x4 1x4 2x2 2x4 1x4 1x1 1x4 1x4 1x4 1x4 1x1 1x4 1x4 1x4 Same as Map Image Source: RADARSAT International, 1995, RADARSAT Illuminated – Your Guide to Products and Services, RADARSAT International Canada Centre for Remote Sensing, Natural Resources Canada General Characteristics Each pixel is represented by I and Q complex data. Must be processed into an image. Retains optimum resolution. Oriented in orbit path. Must be geometrically corrected if required for mapping. Lower sample spacing than SGF Retains full beam resolution. SGF product is processed to North up and corrected to a map projection. SGF product is corrected using GCPs and a DEM. Best positional product. Georeferenced Products Image Products ◆ Lines and pixels oriented to radar system (e.g. SGF, SGX product for RADARSAT). - line direction is azimuth direction of radar - pixel direction is range direction of radar ◆ ◆ Geographic location of pixels is approximated based on locally spherical elliptical Earth at sea level and typically stored in the product header. - typically based on orbit models only, no geocoded control points used. - referred to as systematic georeferenced. Can be in slant or ground range geometry at a variety of pixel spacings. - variety of terminology used for different satellites slide 9) Canada Centre for Remote Sensing, Natural Resources Canada Table 3.2 - Comparable Products Between Different Satellites RAD ARSAT ERS Europe ERS North America SPOT Landsat Path Image (SGF) Precison Image Georeferenced (PRI) Georeferenced Fine Resolution (SGF) 1B Path Oriented Systematic OR Precision Correction Path Image Plus (SGX) N/A N/A N/A N/A Map Image (SSG) Geocoded Image (GEC) Systematically Geocoded (SSG) 2A Map Oriented Systematic Correction Precision Map Image (SPG) Terrain Geocoded Image (GTC) Precision Geocoded (SPG) 2B Map Orientated Precision Correction Signal Data Raw 1 Raw 1 1A 2 Raw 2 Single Look Complex (SLC) Single Look Complex (SLC) Single Look Complex (SLC) N/A N/A 1 2 SAR Signal Data cannot be viewed as an image Optical RAW data (SPOT, Landsat) can be viewed as an image Source: RADARSAT International, 1995, RADARSAT Illuminated – Your Guide to Products and Services Canada Centre for Remote Sensing, Natural Resources Canada Geocoded Products Systematically Geocoded or Map Image (RADARSAT - SSG) ◆ Product is processed to “North Up” and corrected to a map projection. ◆ Image may be converted to one of a large number of map projections. ◆ Sample spacing remains as in original data. Canada Centre for Remote Sensing, Natural Resources Canada Geocoded Products Precision Geocoded or Precision Map Image (RADARSAT - SPG) ◆ Product is further processed to correct the geographic positional data based on use of Digital Elevation Terrain Model and a number of precisely surveyed ground control points within the imaged area. ◆ Data format and map projections same as for SSG. ◆ Sample spacings remain as in original data. ◆ Variety of terminology used for different satellites (see Table 9) Canada Centre for Remote Sensing, Natural Resources Canada