Dr. Sandra L. Cruz Pol

Transcription

1 OUTLINE INTRODUCTION TO MICROWAVE REMOTE SENSING INEL 8695/6669 Dr. Sandra Cruz Pol Microwave Remote Sensing INEL 6669/8695 Dept. of Electrical & Computer Engineering, UPRM, Mayagüez, PR Importance of Microwaves Sensor types: passive/active Radiometers RADARS Electromagnetic Spectrum Atmospheric windows Brief history Applications 1 2 WHY MICROWAVES? Capability to penetrate clouds and, to some extent, rain. Independence of the sun as a source of illumination. Provides info about geometry and bulk-dielectric properties.(e.g. salinity) stages of El Niño WHY MICROWAVES? 30 GHz 300 MHz PENETRATION DEPTH VS. SOIL MOISTURE Penetrate more deeply into vegetation than optical waves. Penetrate into ground (more into dry than wet soil). Visible and IR sensors can sometimes be used to complement this information 5 6 Atmosphere 1

2 IR (TOP) VERSUS MICROWAVES (BOTTOM) ELECTROMAGNETIC SPECTRUM WAVE PENETRATION DEPENDS ON FREQUENCY SOIL PENETRATION [ Aplicaciones: mapas zonas propensas a fuegos SNOW MICROWAVE PENETRATION Aplicación: mapas de barcos icebreakers, estudios climáticos. Why study Clouds? Affect Earth s radiation budget Improve global climate models (GCM) Improve reliability of forecasts Absorbed (blue area) Transmitted (white) 11 Atmospheric Windows W Ka X 12 Atmosphere 2

3 MICROWAVE REMOTE SENSING SENSORS 1. Passive Uses of radiometers to study the Earth Passive sensors are called microwave radiometers, which receive and detect the radiation emitted from various objects on the earth 2. Active Uses RADAR (RAdio Detection And Ranging) to study Earth Active microwave remote sensor illuminates the ground with microwave radiation and then receives the backscattered energy from the object. Some of the active microwave remote sensors are : Radars: CW, Pulse, Doppler, FM, Side looking airborne radar (SLAR), Synthetic aperture radar (SAR) Wind scatterometer Altimeter Polarimeter WHAT IS RADIOMETRY? All objects radiate EM energy. Radiometry measures of natural EM radiation from objects; earth, ice, plants... WHERE DOES ENERGY GOES? Energy (EM waves) received at the Earth from the Sun is absorbed (atmosphere, clouds, earth, ocean ) scattered transmitted Absorbed energy is transformed into thermal energy. Thermodynamic balance through emission, absorption, is called RT=Radiative Transfer Microwave Radiometer (~70% of the time) (Arecibo Observatory works as radar too!) Microwave Radar (Tropical Rainfall Measuring Mission (TRMM) satellite) Global Precipitation Measurement (GPM) Atmosphere 3

4 HISTORY OF RADARS Henry Hertz, st radio experiment, reflections confirmed experimentally that an electric spark propagates electromagnetic waves into space. 1890, Tesla illuminated a vacuum tube wirelessly having transmitted energy through the air using a Tesla coil to change 60Hz into hi-freq Marconi patent for radio, 1986 in England, using 17 patents from Tesla Pulse radars to measure height of ionosphere unintentional detection of airplanes 1943 the Supreme Court overturned Marconi's patent in favor of Tesla. WWII- detecting ships and aircraft. Used PPI displays. MIT- developed magnetron hi-power Tx and klystron Lo-power source 1938 Altimeter airborne FM radars at 400MHz to measure altitude SLAR finer resolution cause antennas length up to 15 m fixed to fuselage. Airplane motion produced a scan. HISTORY OF RADARS Side Looking Aperture Radar (SLAR) Range resolution =>pulse width Azimuth resolution=> antenna size PPI= Plan position indicator Sea Ice and Iceberg Detection By SLAR (Side Looking Airborne Radar) Light blue- sea ice Green -open water 21 HISTORY OF RADARS SAR fine resolution Doppler, pixel dimension in the along track direction independent of distance from radar, antenna could be much smaller. [Complex processing to produce an image.] Scatterometer radar that measures scattering coefficient, σ. (In ocean, scatter is proportional to wind speed.) 1950s 1 st U.S. weather radars 1970 Doppler becomes major technique for meteorology. NEXRAD RADARSAT is a Synthetic Aperture Radar (SAR) at C-band. Used for oceanic oil spill and ice sheet monitoring. A target's position along the flight path determines the Doppler frequency of its echoes: Targets ahead of the aircraft produce a positive Doppler offset; targets behind the aircraft produce a negative offset. As the aircraft flies a distance (the synthetic aperture), echoes are resolved into a number of Doppler frequencies. The target's Doppler frequency determines its azimuth position Seasat-1 Antenna pattern for each of its microwave sensors Atmosphere 4

5 Dr. Sandra L. Cruz Pol SCATTEROMETERS 25 Global View Radar Backscatter by SeaWinds Scatterometer 26 ALTIMETERS HISTORY OF MICROWAVE RADIOMETERS P=kTB only at µλ frequencies EARTH GEOID The geoid is the shape that the surface of the oceans would take under the influence of Earth gravity and rotation alone, in the absence of other influences such as winds and tides 1930s- First radiometers used for radio-astronomy (RAS) 1950s- First radiometers used for terrestrial observations Earth Exploration Satellite Service (EESS) 29 Sandra Cruz-PolRemote Sensing of OceanAtmosphere 30 5

6 WATER ABSORPTION MEASUREMENTS RADIOMETERS circa 1945 A Radiation Laboratory rooftop crew use microwave radiometer equipment pointed at the sun to measure water absorption by the atmosphere. Atop Building 20 (from left): Edward R. Beringer, Bob L. Kyhl, Arthur B. Vane, and Bob H. Dicke (Photo from Five Years at the Radiation Laboratory) WHY MONITOR WV? Water vapor is one of the most significant constituents of the atmosphere since it is the means by which moisture and latent heat are transported to cause "weather". Water vapor is also a greenhouse gas that plays a critical role in the global climate system. This role is not restricted to absorbing and radiating energy from the sun, but includes the effect it has on the formation of clouds and aerosols and the chemistry of the lower atmosphere. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, it is one of the least understood and poorly described components of the Earth's atmosphere Atmosphere 6

7 ELECTROMAGNETIC SPECTRUM IEEE MICROWAVE RADAR BANDS 39 BAND Designation HF VHF UHF Nominal Frequency Range 3-30 MHz MHz MHz SPECIFIC Bands MHz MHz L 1-2 GHz GHz S 2-4 GHz GHz > C 4-8 GHz GHz X 8-12 GHz GHz Ku K GHz GHz GHz GHz Ka GHz GHz V GHz GHz W millimeter GHz GHz GHz Airport Millimeter Wave scanners use 24.25GHz-30GHz frequency range (wavelength 10-12mm) (millimeter) Atmosphere 7

8 Dr. Sandra L. Cruz Pol RADARS SLAR SAR Resolution Sandra Cruz-PolRemote Sensing of OceanAtmosphere 8

9 49 50 SOUNDERS = TEMPERATURE PROFILES On location at the National Center for Atmospheric Research (NCAR) in Texas. A launch crew prepares a 60-GHz atmospheric sensing receiver. Once lofted airborne by balloon, the receiver remotely sensed the temperature profile at different altitudes. These experiments evolved into the Nimbus series of NASA satellites, which later became part of the National Oceanic and Atmospheric Administration's (NOAA) satellite weather forecasting system, also used by NASA. 52 MICROWAVE TEMPERATURE PROFILER ATMOSPHERIC IMAGERS is a microwave radiometer that measures thermal emission from oxygen molecules along a line of sight that is scanned in elevation angle. Knowledge gained in developing this radiometers are useful in developing radiometers for unstart-prevention systems in high-speed (up to mach 2.4) civil-transport aircrafts Checking an instrument that is the direct forerunner of today's operational satellite microwave atmospheric imagers used by NOAA Atmosphere 9

10 MODERN MICROWAVE WATER RADIOMETER (MWR) Provides time-series measurements of columnintegrated amounts of water vapor and liquid water. The instrument itself is essentially a sensitive microwave receiver. That is, it is tuned to measure the microwave emissions of the vapor and liquid water molecules in the atmosphere at specific frequencies. (~22 GHz) 55 TRUCK MOUNTED RADIOMETER This truck-mounted microwave radiometer system measures surface soil moisture at L, S and C bands. 56 EL NIÑO (ENSO) FROM SPACE stages of El Niño 58 GPM follows TRMM- launch Feb 2014 Launched in Atmosphere 10

11 Future Climate Change science/future.html# 61 MEDICAL APPLICATIONS Microwave Radiometry can be used for the detection of different diseases. Madison, WI- tumor-detection system exploits the large dielectric contrast between normal tissues and malignant tumors at microwave frequencies. Clinical trials at Moscow oncological centers, conducted in over 1000 patients have shown that breast cancer detective ability of microwave radiometry is ~90%. Microwave Radiation used for treatment. The microwave procedure used a finely focused beam which heats up and kills tumour cells. The trial is being organised at two centres in the US, in Palm Beach, Florida, and the Harbor UCLA Medical Centre in California NASA TOPEX/POSEIDON AND JASON(S) Altimeter on board measures sea levels with accuracy to better than 5 cm! One of the contributions to the altimetric delay is the wet path delay caused by tropospheric water vapor in the altimetric signal path. The wet path delay is the additional time that it takes for the signal to pass through the water vapor. If this contribution is not subtracted from the measured altimetric delay, this additional time will introduce error to the measured sea surface height NASA JASON 1-3 EL NIÑO AS MEASURED BY T/P Downward-looking water vapor radiometer onboard the altimeter satellite measures microwave radiation at several different frequencies, 18 GHz, 21 GHz, and 37 GHz. These frequencies were chosen because radiances at these frequencies are sensitive to atmospheric water vapor and liquid water Atmosphere 11

12 WEATHER APPLICATIONS: RADAR COLLABORATIVE ADAPTIVE SENSING OF THE ATMOSPHERE (CASA) 10,000 ft 1 km 2 km 3.05 km 4 km snow wind tornado gap 5.4 km Horz. Scale: 1 = 50 km Vert. Scale: 1 -=- 2 km earth surface RANGE (km) 67 Earth curvature effects prevent 72% of the troposphere below 1 km from being observed CASA NSF-ERC DCAS - Distributed Collaborative Adaptive (Weahter Radar) System UPRM Atmosphere 12