1. Lecture 5: Sensors and Orbits Professor Menglin Jin San Jose State University

2. Sensor types (classification) in the following two diagrams

4. Most remote sensing instruments (sensors) are designed to measure photons we concentrate the discussion on optical-mechanical-electronic radiometers and scanners, leaving the subjects of camera-film systems and active radar for consideration elsewhere

5. Non-Photographic Sensor Systems 1800 Discovery of the IR spectral region by Sir William Herschel. 1879 Use of the bolometer by Langley to make temperature measurements of electrical objects. 1889 Hertz demonstrated reflection of radio waves from solid objects. 1916 Aircraft tracked in flight by Hoffman using thermopiles to detect heat effects. 1930 Both British and Germans work on systems to locate airplanes from their thermal patterns at night. 1940 Development of incoherent radar systems by the British and United States to detect and track aircraft and ships during W.W.II. 1950's Extensive studies of IR systems at University of Michigan and elsewhere. 1951 First concepts of a moving coherent radar system. 1953 Flight of an X-band coherent radar. 1954 Formulation of synthetic aperture concept (SAR) in radar. 1950's Research development of SLAR and SAR systems by Motorola, Philco, Goodyear, Raytheon, and others. 1956 Kozyrev originated Frauenhofer Line Discrimination concept. 1960's Development of various detectors which allowed building of imaging and non-imaging radiometers, scanners, spectrometers and polarimeters. 1968 Description of UV nitrogen gas laser system to simulate luminescence.

6. Passive and Active Sensors Passive Sensor: energy leading to radiation received comes from an external source, e.g., the Sun Active Sensor energy generated from within the sensor system is beamed outward, and the fraction returned is measured; radar is an example

7. Imaging and non-imaging sensor Non-imaging: measures the radiation received from all points in the sensed target, integrates this, and reports the result as an electrical signal strength or some other quantitative attribute, such as radiance Imaging the electrons released are used to excite or ionize a substance like silver (Ag) in film or to drive an image producing device like a TV or computer monitor or a cathode ray tube or oscilloscope or a battery of electronic detectors

8. Principal: photoelectric effect There will be an emission of negative particles (electrons) when a negatively charged plate of some appropriate light-sensitive material is subjected to a beam of photons. The electrons can then be made to flow as a current from the plate, are collected, and then counted as a signal Albert Einstein’s experiment (see lecture 2) Thus, changes in the electric current can be used to measure changes in the photons (numbers; intensity) that strike the plate (detector) during a given time interval. The kinetic energy of the released photoelectrons varies with frequency (or wavelength) of the impinging radiation different materials undergo photoelectric effect release of electrons over different wavelength intervals; each has a threshold wavelength at which the phenomenon begins and a longer wavelength at which it ceases.

10. two broadest classes of sensors Passive sensor energy leading to radiation received comes from an external source, e.g., the Sun Active Sensor energy generated from within the sensor system is beamed outward, and the fraction returned is measured Example: radar

11. Radiometer is a general term for any instrument that quantitatively measures the EM radiation in some interval of the EM spectrum spectrometer When the radiation is light from the narrow spectral band including the visible, the term photometer can be substituted. If the sensor includes a component, such as a prism or diffraction grating, that can break radiation extending over a part of the spectrum into discrete wavelengths and disperse (or separate) them at different angles to an array of detectors

12. spectroradiometer The term spectroradiometer is reserved for sensors that collect the dispersed radiation in bands rather than discrete wavelengths Most air/space sensors are spectroradiometers.

13. Moving further down the classification tree, the optical setup for imaging sensors will be either an image plane or an object plane set up depending on where lens is before the photon rays are converged (focused), as shown in this illustration.

14. Field of View (FOV) Sensors that instantaneously measure radiation coming from the entire scene at once are called framing systems. The eye, a photo camera, and a TV vidicon belong to this group. The size of the scene that is framed is determined by the apertures and optics in the system that define the field of view, or FOV

15. Scanning System If the scene is sensed point by point (equivalent to small areas within the scene) along successive lines over a finite time, this mode of measurement makes up a scanning system. Most non-camera sensors operating from moving platforms image the scene by scanning

16. Cross-Track Scanner the Whiskbroom Scanning A general scheme of a typical Cross-Track Scanner

17. Essential Components of Cross-track Sensor 1) a light gathering telescope that defines the scene dimensions at any moment (not shown) 2) appropriate optics (e.g., lens) within the light path train 3) a mirror (on aircraft scanners this may completely rotate; on spacecraft scanners this usually oscillates over small angles) 4) a device (spectroscope; spectral diffraction grating; band filters) to break the incoming radiation into spectral intervals 5) a means to direct the light so dispersed onto an array or bank of detectors 6) an electronic means to sample the photo-electric effect at each detector and to then reset the detector to a base state to receive the next incoming light packet, resulting in a signal stream that relates to changes in light values coming from the ground targets as the sensor passes over the scene 7) a recording component that either reads the signal as an analog current that changes over time or converts the signal (usually onboard) to a succession of digital numbers, either being sent back to a ground station Note: most are shared with Along Track systems

18. pixel The cells are sensed one after another along the line. In the sensor, each cell is associated with a pixel that is tied to a microelectronic detector Pixel is a short abbreviation for Picture Element a pixel being a single point in a graphic image Each pixel is characterized by some single value of radiation (e.g., reflectance) impinging on a detector that is converted by the photoelectric effect into electrons

19. NASA, Terra & Aqua –launched 1999, 2002 –705 km polar orbits, descending (10:30 a.m.) & ascending (1:30 p.m.) Sensor Characteristics –36 spectral bands (490 detectors) ranging from 0.41 to 14.39 µm –Two-sided paddle wheel scan mirror with 2330 km swath width –Spatial resolutions: 250 m (bands 1 - 2) 500 m (bands 3 - 7) 1000 m (bands 8 - 36) –2% reflectance calibration accuracy –onboard solar diffuser & solar diffuser stability monitor –12 bit dynamic range (0-4095) MODerate-resolution Imaging Spectroradiometer (MODIS)

20. MODIS Onboard Calibrators Fold Mirror Space View Port Blackbody Spectral Radiometric Calibration Assembly Nadir (+z) Solar Diffuser Scan Mirror

21. MODIS Optical System Visible Focal Plane Tra ck Sc an SWIR/MWI R Focal Plane NIR Focal Plane LWIR Focal Plane

22. Shortwave IR/Midwave IRVisible Longwave InfraredNear-infrared Four MODIS Focal Planes

23. MODIS Cross-Track Scan on Terra MODIS_Swath MISR_Swath

24. Along-track Scanner pushbroom scanning the scanner does not have a mirror looking off at varying angles. Instead there is a line of small sensitive detectors stacked side by side, each having some tiny dimension on its plate surface; these may number several thousand

25. Along-track, or Pushbroom, Multispectral System Operation

26. Multi-angle Imaging SpectroRadiometer (MISR) NASA, EOS Terra –Launched in 1999 –polar, descending orbit of 705 km, 10:30 a.m. crossing Sensor Characteristics –uses nine CCD-based push- broom cameras viewing nadir and fore & aft to 70.5° –four spectral bands for each camera (36 channels), at 446, 558, 672, & 866 nm –resolutions of 275 m, 550 m, or 1.1 km Advantages –high spectral stability –9 viewing angles helps determine aerosol by µ dependence (fixed  )

27. MISR Pushbroom Scanner Orbital characteristics –400 km swath –9 day global coverage –7 min to observe each scene at all 9 look angles Family portrait –9 MISR cameras –1 AirMISR camera

28. MISR Provides New Angle on Haze In this MISR view spanning from Lake Ontario to Georgia, the increasingly oblique view angles reveal a pall of haze over the Appalachian Mountains

29. spectral resolution The radiation - normally visible and/or Near and Short Wave IR, and/or thermal emissive in nature - must then be broken into spectral intervals, i.e., into broad to narrow bands. The width in wavelength units of a band or channel is defined by the instrument's spectral resolution The spectral resolution achieved by a sensor depends on the number of bands, their bandwidths, and their locations within the EM spectrum

30. Spectral filters Absorption and Interference. Absorption filters pass only a limited range of radiation wavelengths, absorbing radiation outside this range. Interference filters reflect radiation at wavelengths lower and higher than the interval they transmit. Each type may be either a broad or a narrow bandpass filters. This is a graph distinguishing the two types.

31. Orbits

32. The Afternoon Constellation “A-Train ”  The Afternoon constellation consists of 7 U.S. and international Earth Science satellites that fly within approximately 30 minutes of each other to enable coordinated science  The joint measurements provide an unprecedented sensor system for Earth observations

33. Video Terra_orbit

34. Satellite Orbits At what location is the satellite looking? When is the satellite looking at a given location? How often is the satellite looking at a given location? At what angle is the satellite viewing a given location? Video: EOS orbits

35. Low Earth Orbit Concepts Equator South Pole Ground track Ascending node Inclination angle Descending node Orbit Perigee Apogee Orbit

36. Sun-Synchronous Polar Orbit Satellit e Orbit Earth Revolution Satellite orbit precesses (retrograde) –360° in one year Maintains equatorial illumination angle constant throughout the year –~10:30 AM in this example Equatorial illumination angle

37. Sun-Synchronous Orbit of Terra

38. Period of orbit Valid only for circular orbits (but a good approximation for most satellites) Radius is measured from the center of the Earth (satellite altitude+Earth’s radius) Accurate periods of elliptical orbits can be determined with Kepler’s Equation T 2 = r 3 4242 Gm e Period of orbit Gravitational constantMass of the Earth Radius of the orbit

39. The orbital period of a satellite around a planet is given by where  0 = orbital period (sec) R p =planet radius (6380 km for Earth) H=orbit altitude above planet’s surface (km) g s =acceleration due to gravity (0.00981 km s -2 for Earth) Definition of Orbital Period of a Satellite

40. Spacing Between Adjacent Landsat 5 or 7 Orbit Tracks at the Equator

41. Timing of Adjacent Landsat 5 or 7 Coverage Tracks Adjacent swaths are imaged 7 days apart

42. Types of orbits Sunsynchronous orbits: An orbit in which the satellite passes every location at the same time each day –Noon satellites: pass over near noon and midnight –Morning satellites: pass over near dawn and dusk –Often referred to as “polar orbiters” because of the high latitudes they cross –Usually orbit within several hundred to a few thousand km from Earth

43. Sun Synchronous (Near Polar) Video –TERRA/AQUA

44. Sunsynchronous image (SMMR)

45. Sunsynchronous image (AVHRR)

46. Types of orbits Geostationary (geosynchronous) orbits: An orbit which places the satellite above the same location at all times –Must be orbiting approximately 36,000 km above the Earth –Satellite can only “see” part of hemisphere

47. Geostationary Image (GOES-8)

49. Space-time sampling Geostationary –Fixed (relatively) field of view –View area of about 42% of Earth’s surface Sunsynchronous –Overlapping views –See each point at several viewing angles Other orbits (“walking orbits”) –Passes each location at a different time of day –Earth Radiation Budget Satellite –Useful when dirunal information is needed

50. qA precessing low-inclination (35 ° ), low-altitude (350 km) orbit to achieve high spatial resolution and capture the diurnal variation of tropical rainfall –Raised to 402 km in August 2001 Tropical Rainfall Measuring Mission Orbit (Precessing)

51. TRMM Coverage 1 day coverage2 day coverage

52. Landsat 7 Goals & Objectives  Land use and land cover change –Agricultural evaluations, forest management inventories, water resource estimates, coastal zone appraisals –Growth patterns of urban development, Spring run-off contaminants in lakes, land use in tropical rainforests, health of temperate conical forests  Vegetation patterns –Annual cycle of vegetation dynamics, drought stress, and flooding  Glaciers and snow cover –Growth and retreat  Geological surveys –Volcanic hazards Launched April 15, 1999

53. Enhanced Thematic Mapper Plus (ETM+) NASA & USGS, Landsat 7 –launched April 15, 1999 –705 km polar orbit, descending (10:00 a.m.) Sensor Characteristics –7 spectral bands ranging from 0.48 to 11.5 µm –1 panchromatic band (0.5-0.9 µm) –cross-track scan mirror with 185 km swath width –Spatial resolutions: 15 m (panchromatic) 30 m (spectral) –Calibration: 5% reflectance accuracy 1% thermal IR accuracy onboard lamps, blackbody, and shutter solar diffuser

54. Landsat Thematic Mapper Bands Landsat collects monochrome images in each band by measuring radiance & reflectance in each channel –When viewed individually, these images appear as shades of gray

55. TRMM Satellite

56. 1998-2005 Mean Monthly Rainfall (5°x5°)

57. Polar-Orbiting Satellite in Low Earth Orbit (LEO) Example from Aqua

58. Orbital Characteristics of Selected Missions Low Earth Orbit & Precessing Missions

59. Earth Science Mission Profile 1997-2003 eospso.gsfc.nasa.gov

60. Earth Science Mission Profile 2004-2010 eospso.gsfc.nasa.gov

61. The Afternoon Constellation “A-Train ”  The Afternoon constellation consists of 7 U.S. and international Earth Science satellites that fly within approximately 30 minutes of each other to enable coordinated science  The joint measurements provide an unprecedented sensor system for Earth observations

62. Satellites in Geosynchronous Orbits are used as Relay Satellites for LEO Spacecraft Imaging System (e.g., Landsat) Communication relay system Communication relay system (e.g., TDRSS) GEO LEO Ground station

63. Geosynchronous Meteorological Satellites WMO Member States

64. Hurricane Wilma October 2005

65. Sample Calibration Curve Used to Correlate Scanner Output with Radiant Temperature Measured by a Radiometer

66. The human eye is not sensitive to ultraviolet or infrared light –To build a composite image from remote sensing data that makes sense to our eyes, we must use colors from the visible portion of the EM spectrum—red, green, and blue Color Composites

67. Chesapeake & Delaware Bays R=0.66 µm G=0.56 µm B=0.48 µm Balti more Washi ngton May 28, 1999

68. “False Color” Composite Image To interpret radiance measurements in the infrared portion of the electromagnetic spectrum, we assign colors to the bands of interest and then combine them into a “false color” composite image

69. Terra ASTER Launched December 18, 1999 MODIS CERES MISR MOPITT

70. NASA & MITI, Terra –705 km polar orbit, descending (10:30 a.m.) Sensor Characteristics –14 spectral bands ranging from 0.56 to 11.3 µm –3 tiltable subsystems for acquiring stereoscopic imagery over a swath width of 60 km –Spatial resolutions: 15 m (bands 1, 2, 3N, 3B) 30 m (bands 4 - 9) 90 m (bands 10 - 14) –4% reflectance calibration accuracy (VNIR & SWIR) –2 K brightness temperature accuracy (240-370 K) Advanced Spaceborne Thermal Emission & Reflection Radiometer (ASTER) SWIR VNIR (1,2,3N) VNIR (3B)TIR

71. Comparison of Landsat 7 and ASTER

72. Synergy Between Terra and Landsat 7 Data (same day 705 km orbits ~ 30 minutes apart) spatial resolution (275, 550, 1100 m) Landsat ETM+ input to Terra data Vegetation classification for MODIS & MISR biophysical products Focus on global change hotspots detected by MODIS & MISR Linking Terra observations with 34+ year Landsat archive Radiometric rectification of MODIS data 183 km 2330 km swath width spatial resolution (250, 500, 1000 m) global coverage  2 days 360 km global coverage  9 days spatial resolution (15, 30, 60 m) Landsat 7 16 day orbital repeat global coverage  seasonally spatial resolution (15, 30, 90 m) ASTER 45-60 day orbital repeat global coverage  months to years 60 km swath MODIS MISR Terra input to Landsat ETM+ data Use of MODIS & MISR for improved atmospheric correction of ETM+ Use of MODIS & MISR for temporal interpolation of ETM+ data Cross-calibration of ASTER, MISR, and MODIS

73. Aqua Launched May 4, 2002 MODIS CERES AIRS AMSR-E AMSU HSB

74. NASA, Aqua –launched May 4, 2002 –705 km polar orbits, ascending (1:30 p.m.) Sensor Characteristics –12 channel microwave radiometer with 6 frequencies from 6.9 to 89.0 GHz with both vertical and horizontal polarization –Conical scan mirror with 55° incident angle at Earth’s surface –Spatial resolutions: 6 x 4 km (89.0 GHz) 75 x 43 km (6.9 GHz) –External cold load reflector and a warm load for calibration 1 K T b accuracy Advanced Microwave Scanning Radiometer (AMSR-E)

75. AMSR-E Conical Scan on Aqua

76. AMSR-E Composite Sea Surface Temperature June 2002 -2 28 °C 35 Orange colors denote temperature necessary for hurricane formation

77. Satellite online visualization (class Activity) Satellite rainfall observations are very useful to reveal the rain intensity and spatial distribution over the globe. Tropical rainfall measurement mission (TRMM) is one NASA program to monitor rainfall from the space bake to 1998. Use the Monthly TRMM and Other Data Sources Rainfall Estimate (3B43 V6) (http://disc2.nascom.nasa.gov/Giovanni/tovas/TRMM_V6.3B43.sh tml), to answer the following questions: –Plot spatial distribution of rainfall at CA area (25-40°N, 110-125°W) using data from May 1998 to May 2009. Where do you see the highest rainfall in this area? How much there? –Plot the time series of accumulated rainfall for the same CA area above during the same time. Which month does CA have the highest rainfall and which month CA have the lowest rainfall? How much are the highest and lowest rainfall respectively? –Plot the rainfall over the globe spatial distribution (180°W-180°E, 50°N-50°S) for July 2008 and December 2008, respectively. Describe at least three major differences of the rainfall pattern of these two months.