MICROW~1.PPT

Canada Centre for Remote Sensing, Natural Resources Canada Natural Resources Ressources naturelles Canada Canada MICROWAVE RADAR FUNDAMENTALS OF MICROWAVE RADAR  Introduction to Microwave Radar:  Definition  Merits and demerits  Equation  Instrumentation  Image configuration Natural Resources...

Canada Centre for Remote Sensing, Natural Resources Canada Natural Resources Ressources naturelles Canada Canada MICROWAVE RADAR FUNDAMENTALS OF MICROWAVE RADAR  Introduction to Microwave Radar:  Definition  Merits and demerits  Equation  Instrumentation  Image configuration Natural Resources Ressources naturelles Canada Canada Definition  RADAR is an acronym for RAdio Detection And Ranging:  Irradiates a target at particular microwave frequency and measures energy returned at same frequency after scattering has occured;  Measured energy is referred to as “backscattered energy” or energy scattered by target that is detected by the sensor;  Has three primary functions:  Transmits microwave (radio) signals towards a scene;  Receives the portion of the transmitted energy backscattered from the scene; and  Observes the strength (detection) and the time delay (ranging) of the return signals.  Thus, the measurable quantities are:  Time delay of return signal (range/distance of object)  Strength of backscattered energy Definition  Thus, the measurable quantities are:  Time delay of return signal (range/distance of object)  Strength of backscattered energy (object size, geometry/orientation, surface roughness and dielectric properties; frequency used and strength of transmitted signal);  Radar is an active remote sensing system because it provides its own energy source;  uses the microwave portion of the electromagnetic spectrum, from a frequency of 0.3 GHz to 300 GHz, or in wavelength terms, from 1 m to 1 mm;  Characterized by polarization, and by frequency or wavelength (inversely proportional to frequency;  Ranges from X-band (2.4-3.8cm or 12.5 – 8GHz); Cband (3.8 – 7.5cm or 8 – 4GHz); S-band (7.5 – 15cm or 4 – 2 GHz), L-band (15 – 30 cm or 2 – 1 GHz); Canada Centre for Remote Sensing, Natural Resources Canada Electromagnetic Spectrum Canada Centre for Remote Sensing, Natural Resources Canada The electromagnetic spectrum with microwave bands inset. Credit: NASA SAR Handbook. Merits and Demerits  Controllable source of illumination  “sees" through cloud and rain, dry soil, canopy (high penetrative capability)  Day and night capability (Independent of solar radiation)  Images can be high resolution (3 - 10 m)  Different features are portrayed or discriminated compared to visible sensors (drainage and topography)  Some surface features can be seen better in radar images: – ice, ocean waves – soil moisture, vegetation mass – man-made objects, e.g. buildings – geological structures Radar Equation  Describes the relationship between radar, target and received signal;  The simplest equation for dual purpose antenna is given by: 2  Pr = PtG2  /(4 )3R4  Pr = Received power  Pt = Transmitted power  G = Antenna gain  R = Range to target  = Radar wavelength  = Radar cross-section  Radar cross section of the target is dependent on target parameters (surface roughness, geometry and dielectric properties) and system parameters (frequency/wavelength, incident angle and polarisation) Canada Centre for Remote Sensing, Natural Resources Canada Basic elements of a radar system http://www.radartutorial.eu/01.basics/Radar %20Principle.en.html  Most radar systems use a single antenna to transmit and receive signals;  Transmission is done in “short bursts” or pulses; and  Antenna is switched alternatively between transmission and reception of signal Canada Centre for Remote Sensing, Natural Resources Canada RADAR - Radio Detection And Ranging Ra ng e Pul se Echo Canada Centre for Remote Sensing, Natural Resources Canada SAR Flight Geometry Swath width dir n tio ec Altitude t gh i l F Sl an t r an ge ar Ne e ng a r Incident Angle r Ground Range zim h ut A Source: Adapted from K. Raney Canada Centre for Remote Sensing, Natural Resources Canada Fa e ng a r Radar image configuration  The radar transmits pulses at the pulse repetition frequency, PRF, and for each pulse the backscatter return from the ground is sampled in range at the analog to digital (A/D) sampling frequency;  The radar operation is coherent, which means that both the return magnitude and phase (with respect to the transmitted signal) are sampled. For each range sample the in-phase and quadrature values (I and Q) are stored;  The raw data file is thus a two dimensional array of complex values (with I as the real part and Q as the imaginary part);  This two-dimensional data set is then processed to form an image.i.e. a visual representation of the amount of microwave energy backscattered from the earth surface;  It is also a single frequency representation of the earth which highlights changes in the terrain’s roughness, relief and moisture levels  Canada Centre for Remote Sensing, Natural Resources Canada Radar image configuration  The content of the image is influenced by system configuration and surface properties;  Low backscatter values are portrayed as dark tones, while high backscatter values appear as bright tones;  These images provide information on targets’ physical properties, unlike the chemical and thermal properties information provided by VNIR and TIR images;  A thorough understanding of the influence of target and system parameters is required for interpreting radar images;  Canada Centre for Remote Sensing, Natural Resources Canada Spaceborne SARs The viewing geometry of a spaceborne SAR, in comparison to an airborne SAR with a similar swath width, varies only a few degrees and thus provides a more uniform illumination geometry over the whole swath. Depending on the orbital parameters, a spaceborne SAR can collect data more quickly over larger areas than airborne systems. Frequency of coverage is set by orbit constraints and imaging modes of the radar. Revisit for typical spaceborne SAR is between 3-35 days. Corrections must be made in processing for the effects of earth curvature, earth rotation and orbital variations. The first civilian spaceborne SAR was SEASAT (USA) in 1978, followed by Almaz (USSR/Russia), ERS-1 (Europe), J-ERS-1 (Japan), ERS-2 (Europe) and RADARSAT-1 (Canada). Canada Centre for Remote Sensing, Natural Resources Canada Past Orbital SAR Systems Parameters Seasat SIR-A SIR-B Almaz SIR-C/X SAR ERS-1 JERS-1 Country USA USA USA USSR USA Europe Japan Launch Date Jun ‘78 Oct ‘84 Mar ‘91 Apr ‘94 Jul ’91 Feb ‘92 Lifetime (design) 8 days 2 years each 11 days 3 years 2 years Band 3 months L Nov ‘81 2.5 days L L S L, C, X C L Wavelength (cm) 23.5 23.5 23.5 10 23.9, 5.7, 9.6 5.7 23.5 Polarization HH HH HH HH VV HH Nominal Incident Angle (°) Nominal Ground Range Resolution (m) Nominal Azimuth Resolution (m) No. of Looks 23 50 15 - 64 30 - 60 L and C Quad Pol X (VV) 15 - 50 23 38 25 40 25 15 - 30 10 - 26 26 18 25 40 17 – 58 15 30 28 18 4 6 4 >4 4 3 3 Swath Width (km) 100 50 10 - 60 20 - 45 15 – 60 100 75 Repeat Cycle (days) 17, 3 nil nil nil nil 3, 35, 176 44 Canada Centre for Remote Sensing, Natural Resources Canada Current and Planned Orbital SAR Systems Parameters ERS-2 RADARSAT 1 Envisat 1 ASAR ALOS PALSAR SAOCOM RADARSAT 2 Country Europe Canada Europe Japan Argentina Canada Launch Date Apr ‘95 Nov. 1995 2001 2002 2003 2003 Lifetime (design) Band 3 years 5 years 5 years 3-5 years 5 years 5 years C C C L L C Wavelength (cm) Polarization Nominal Incident Angle (°) Nominal Ground Range Resolution (m) 5.7 5.7 5.6 23.6 23 5.6 VV 23 HH 10 – 59 Note 1 15 – 45 Note 2 8-60 Note 3 15-40 Note 4 10 – 60 26 10 – 100 30 – 1000 10-100 10-100 3 – 100 Nominal Azimuth Resolution (m) No. of Looks 28 9 – 100 30 – 1000 10-100 10-100 3 – 100 3 1–8 8 2-8 2-8 1–8 Swath Width (km) Repeat Cycle (days) 100 50 – 500 60 – 405 30-350 35-360 10 – 500 35 24 35 46 7 24 1- Envisat polarizations HH or VV or HH+VV or HH+HV or VV+VH 2- ALOS PALSAR polarizations HH or VV or HH+HV or VV+VH or HH+HV+VH+VV HH+HV or VV+VH or HH+HV+VH+VV 3- SAOCOM polarizations HH or VV or 4- RADARSAT-2 polarizations HH or VV or HV or VH or HH+HV or VV+VH or HH+HV+VH+VV Canada Centre for Remote Sensing, Natural Resources Canada