LE/ESSE Payload Design

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1 LE/ESSE Payload Design 3.2 Spacecraft Sensors Introduction to Sensors Earth, Moon, Mars, and Beyond Dr. Jinjun Shan, Professor of Space Engineering Department of Earth and Space Science and Engineering Room 255, Petrie Science and Engineering Building Tel: ext jjshan@yorku.ca Homepage:

2 Introduction Classification of sensor Optical sensors Microwave sensors Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 2

3 Classification of Sensor E = σt 4 λ max = 2898 /T Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 3

4 Passive sensors detect the reflected or emitted electro-magnetic radiation from natural sources Active sensors detect reflected responses from objects which are irradiated from artificially generated energy sources, such as radar. A sensor classified as a combination of passive, non-scanning and non-imaging method is a type of profile recorder, for example a microwave radiometer. A sensor classified as passive, nonscanning and imaging method, is a camera. Sensors classified as a combination of passive, scanning and imaging are classified into image plane scanning sensors, such as TV cameras and solid state scanners, and object plane scanning sensors, such as multispectral scanners (opticalmechanical scanner) and scanning microwave radiometers. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 4

5 An example of an active, non-scanning and non-imaging sensor is a profile recorder such as a laser spectrometer and laser altimeter. An active, scanning and imaging sensor is a radar, for example synthetic aperture radar (SAR), which can produce high resolution, imagery, day or night, even under cloud cover. In remote sensing, the most popular sensors are the camera, solid state scanner, such as the CCD (charge coupled device) images, the multi-spectral scanner and in the future the passive synthetic aperture radar. Laser sensors have recently begun to be used more frequently for monitoring air pollution by laser spectrometers and for measurement of distance by laser altimeters. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 5

6 Most common sensors and their spectral bands Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 6

7 Optical Sensors Those sensors which use lenses in the visible and reflective infrared region, are called optical sensors. Optical sensors are characterized specified by spectral, radiometric and geometric performance. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 7

8 Definitions of Optical Sensor s Characteristics Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 8

9 Spectrometer A spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum. The variable measured is most often the light's intensity but could also, for instance, be the polarization state. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 9

10 Prism spectrometer This Figure shows a simple prism spectrometer for examining a light source with a focusing lens to produce parallel light (plane waves) which is dispersed by the prism. The spectrum of plane waves can be focused onto a photographic plate. The plate must be tilted to keep all the colors in focus because of the change in focal length of the lens with wavelength. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 10

11 Diffraction spectrometer Different diffraction based spectrometers: Reflection optics Refraction optics Fiber optics Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 11

12 Michelson interferometer The Michelson interferometer is the most common configuration for optical interferometry. The Michelson interferometer produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 12

13 Fabry-Pérot interferometer or etalon Fabry-Pérot interferometer or etalon is typically made of a transparent plate with two reflecting surfaces, or two parallel highly-reflecting mirrors. (Technically the former is an etalon and the latter is an interferometer) Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 13

14 Application of Spectrometer In astronomy, spectrographs are widely used. These are installed at the focus of a telescope which may be either in a ground-based observatory or in a spacecraft. The Mars Exploration Rovers each contained a Mini-TES - a Miniature Thermal Emission Spectrometer (i.e. infrared spectrometer). The forthcoming James Webb Space Telescope will contain both a nearinfrared spectrograph (NIRSpec) and a mid-infrared spectrometer (MIRI). This image shows the martian terrain through the eyes of the Mars Exploration Rover Spirit's mini-thermal emission spectrometer, an instrument that detects the infrared light, or heat, emitted by objects. The different colored circles show a spectrum of soil and rock temperatures, with red representing warmer regions and blue, cooler. The mini-thermal emission spectrometer data are superimposed on an image taken by the rover's panoramic camera. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 14

15 Detectors An element which converts the electro-magnetic energy to an electric signal is called a detector. There are various types of detectors with respect to the detecting wavelength. Photo tube and photo multiplier tubes are the examples of the photo emission type which has sensitivity in the region from ultra violet to visible light. Optical excitation types have sensitivity in the infrared region. Photo diode detectors utilize electric voltage from the excitation of electrons, while photo transistor and photo conductive detector utilize electric current. Thermocouple bolometers and pyroelectric bolometers are examples of the thermal effect type, which has sensitivity from near infrared to far infrared regions. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 15

16 Cameras Cameras may work with the visual spectrum or other portions of the electromagnetic spectrum. Examples of space cameras, are the Metric Camera on board the Space Shuttle by ESA, the Large Format Camera also on board the Space Shuttle by NASA, and the KFA 1000 on board COSMOS by Russia. Multispectral cameras with several separate film scenes in the visible and reflective IR, are mainly used for photo-interpretation of land surface covers. Panoramic cameras are used for reconnaissance surveys, surveillance of electric transmission lines, supplementary photography with thermal imagery, etc., because the field of view is so wide. LE-900 reusable space camera is used as part of a Video Guidance Sensor System for docking of the Spartan Satellite. The camera has supported several flights aboard the space shuttle including a variety of satellite applications. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 16

17 Cameras - Russia 1. Luna-3 2. Mars-1 3. Zond-3, Luna-12, Venera-2 4. Mars-5 Orbiter 5. Experimental 6. Experimental 7. Luna-9, Mars-3 Landers 8. Luna-19, Luna Mars-5, Venera-9 Orbiter 10. Earth orbiter (Meteor) 11. Earth orbiter 12. Venera-9 Lander Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 17

18 Long Wave Infrared Camera - Clementine Mass: 2100 grams Size: 15 x 15 x 40 cm Avg. Power 26 W Wavelength: microns Field of View: 1.0 x 1.0 degrees Pixel Format: 128 x 128 The long wave infrared camera for Clementine, a lightweight camera operating in the thermal infrared region of the spectrum. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 18

19 Optical Mechanical Scanner An optical mechanical scanner is a multispectral radiometer by which two dimensional imagery can be recorded using a combination of the motion of the platform and a rotating or oscillating mirror scanning perpendicular to the flight direction. Optical mechanical scanners can be carried on polar orbit satellites or aircraft. Multispectral scanner (MSS) and thematic mapper (TM) of LANDSAT, and Advanced Very High Resolution Radiometer (AVHRR) of NOAA are the examples of optical mechanical scanners. Optical mechanical scanners are composed of an optical system, spectrographic system, scanning system, detector system and reference system. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 19

20 Function of the elements Optical system: Reflective telescope system such as Newton, Cassegrain or Ritchey-Chretien is used to avoid color aberration. Spectrographic system: Dichroic mirror, grating, prism or filter are utilized. Scanning system: rotating mirror or oscillating mirror is used for scanning perpendicular to the flight direction. Detector system: Electromagnetic energy is converted to an electric signal by the optical electronic detectors. Photomultiplier detectors utilized in the near ultra violet and visible region, silicon diode in the visible and near infrared. Reference system: The converted electric signal is influenced by a change of sensitivity of the detector. Therefore light sources or thermal sources with constant intensity or temperature should be installed as a reference for calibration of the electric signal. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 20

21 Multispectral scanner -Skylab Multispectral Scanner (S192). (a) Cutaway diagram. (b) Scanner Optics. (c) Lens system. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 21

22 Atmospheric Sensors Atmospheric sensors are designed to provide measures of air temperature, vapor, atmospheric constituents, aerosols etc. as well as wind and earth radiation budget. Laser Radar or Lidar is an active sensor which is used to measure air pollution, physical characteristics of atmospheric constituents in the stratosphere and its spatial distribution using laser. The theory of laser radar is also utilized to measure distance, so that for this application it is called laser distancemeter or laser altimeter. Laser altimeters have been used by Apollo 15, 16, 17 to provide ranging data for use in determining the altitude of the CSM above the lunar surface. The Clementine Laser Image Detection And Ranging (LIDAR) experiment was designed to measure the distance from the spacecraft to a point on the surface of the Moon. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 22

23 Microwave Sensors Many of the earth observation satellites launched after 1992 are equipped with onboard microwave sensors. Passive and active sensors Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 23

24 Frequency of passive microwave sensor for monitoring major targets - I Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 24

25 Frequency of passive microwave sensor for monitoring major targets - II Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 25

26 Active Sensors Active sensors can be classified into more types in terms of the target with respect to horizontal or vertical polarization. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 26

27 Frequency of active microwave sensor for monitoring major targets Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 27

28 Imaging radar Imaging radar is classified further into Real Aperture Radar (RAR) and Synthetic Aperture Radar (SAR). RAR transmits a narrow angle beam of pulse radio wave in the range direction at right angles to the flight direction (called the azimuth direction) and receives the backscattering from the targets which will be transformed to a radar image from the received signals. The resolution in the range direction depends on the pulse width. The resolution in the azimuth direction is identical to the multiplication of beam width and the distance to a target. As the resolution of azimuth direction increases with shorter wave length and bigger antenna size, a shorter wavelength and a bigger antenna is used for higher azimuth resolution. However as it is difficult to attach such a large antenna, requiring for example a 1 km diameter antenna in order to obtain 25 meters resolution with L band (=25 cm) and 100 km distance from a target, a real aperture radar therefore has a technical limitation for improving the azimuth resolution. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 28

29 Side-looking airborne radar operation Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 29

30 SAR Compared to RAR, Synthetic Aperture Radar (SAR) synthetically increases the antenna's size or aperture to increase the azimuth resolution though the same pulse compression technique as adopted for range direction. Synthetic aperture processing is a complicated data processing of received signals and phases from moving targets with a small antenna, the effect of which is to should be theoretically convert to the effect of a large antenna, that is a synthetic aperture length. In the case of SAR, unsuitability of satellite velocity and attitude will reduce the Doppler effect. Therefore the satellite with SAR is required to be high, because the correction for synthetic aperture processing due to instability at lower altitudes is very difficult. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 30

31 Relationship between RAR and SAR Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 31

32 Characteristics are of importance Two factors of microwave characteristics are of importance: frequency (or wavelength) and polarization. In microwave remote sensing, various wavelengths (or frequency) such as L-band, C-band, X-band, P-band etc. will be used ranging from millimeter wavelengths (1 mm - 1cm) up to about 30 cm. Polarization is defined as the oscillating direction involved in an electric field. Usually transmitted microwave and received microwave will have a choice between horizontal polarization and vertical polarization. Therefore four combinations: HH, HV, VH and VV can be used for SAR. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 32

33 Radarsat 2 Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 33

34 Microwave Radiometer Microwave radiometers or passive type microwave sensors are used to measure the thermal radiation of the ground surface and/or atmospheric condition. Brightness temperature measured by a microwave radiometer is expressed by Reyleigh-Jean's law, which is the resultant energy of thermal radiation from the ground surface and the atmospheric media. Multi-channel radiometers with multipolarization are used to avoid the influences of unnecessary factors to measure the specific physical parameter. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 34

35 Jason Microwave Radiometer The image shows a mapping of preliminary channel 1 antenna temperatures from the first five days of operation. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 35

36 Microwave Scatterometer Microwave scatterometers can measure the received power of surface backscattering reflected from the surface of objects. According to a narrow definition, a microwave scatterometer may be a space borne sensor to measure the two dimensional velocity vectors of the sea wind, while according to the wider definition, it also involves air-borne sensors, as well as ground based sensors to measure the surface backscattering as well as volume scattering, such as rain radar. Microwave scatterometers are classified as two types, pulse type and continuous wave type (CW). The pulse type uses wide band which has restrictions in obtaining a license to operate and in avoid obstructions. CW type has the advantage that the band width can be reduced to 1/100 times that of the pulse type and the price becomes cheaper. SEASAT-SASS (Seasat-A Satellite Scatterometer) is one of the typical scatterometers. SASS has four fixed antennas to transmit the pulse in a fan beam of 14.5 GHz to four different angles, and to receive the backscattering in subdivided cells through a Doppler filter. Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 36

37 3-band microwave scatterometer X-Band:9.6 GHz C-Band:5.4 GHz L-Band:1.2 GHz Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 37

38 Microwave Altimeter Microwave altimeters or radar altimeters are used to measure the distance between the platform (usually satellite or aircraft) and the ground surface. Some applications of microwave altimetry are in ocean dynamics of the sea current, geoid surveys, and sea ice surveys. Therefore, precise measurement of the satellite orbit and the geoid should be carried out. The principle of satellite altimetry Prof. Jinjun Shan Spacecraft Sensor Introduction to Sensors 38