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1 1971 Radar used to map Brazil s Amazon Basin Entire ~ 5M km 2 Discovered major Amazon tributary Found fertile soil Until 1993 estimates of area and rate of deforestation ranged widely (21K 2 80K 2 /yr) 1993 Skole & Tucker published definitive calculation in Science (used Landsat & GIS)

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6 Taking advantage of the latest space technology and Earth observation science, including the 36-year legacy of the US Landsat satellite programme, the Atlas serves to demonstrate the potential of satellite imagery data in monitoring ecosystems and natural resources dynamics. This in turn can provide the kind of hard, evidence-based data to support political decisions aimed at improving management of Africa's natural resources. UNEP 2008

7 Using satellite images, the Insurance Services Office, an industry support organization, last month unveiled a new tool for insurers, involving color-coded maps showing the density of dry grass, trees or dense brush near houses, the irregularities of the local terrain and road access for firefighters. San Diego Union-Tribune Oct. 24, 2004

8 Remote Sensing Basics a tour of the world of remote sensing around you presented by laura rocchio NSF Grant # DUE

9 Remote Sensing Defined Getting a sense of something remotely Acquiring of information about an object without physical contact Observing things from a distance Learning without touching What could be considered remote sensing? Your eyes, medical scans such as x-rays and CT scans, sonar measurements of the seafloor, radar used for speeding tickets

10 Remote Sensing: A Limited Definition The term remote sensing was coined by Evelyn Pruitt, a geographer in the 1950s with the Office of Naval Research. Remote sensing is the science (and to some extent, art) of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted electromagnetic energy and processing, analyzing, and applying that information. CCRS Extensively used in fields of meteorology, oceanography, forestry, agriculture, archaeology, cartography, geology, geography, range management, hydrology, and atmospheric and soil science A tool or a science? Both.

11 Remote Sensing: A Limited Definition Observation of Earth from above, involving the interaction between incoming radiation and targets of interest (including emitted radiation) Here: limited to interaction of energy from the electromagnetic spectrum (blue light through thermal infrared energy, 0.4 to 15 micrometers) with Earth s land surfaces Two types of remote sensing active & passive Active - energy comes from sensor Passive - energy comes source other than sensor (most often the sun) From above towers, planes, satellites

12 Remote Sensing: A Limited Definition Federal remote sensing sensors we are focusing on: Landsat MODIS ASTER

13 Why is remote sensing important? remote sensing is a reality whose time has come. It is a powerful tool that cannot be ignored because of its information potential and the logic implicit in the reasoning processes employed to analyze remotely sensed data. When allied with cartography through the use of information systems, remote sensing techniques can rise above the level of mere technology. This coupling can change our perceptions, our method of data analysis, our models, and our paradigms. Simonett et al., Manual of Remote Sensing Remote sensing is unique in that it can be used to collect fundamental biophysical data, unlike other techniques such as cartography, GIS, and statistics, which rely on data that are already available... If Remote you sensing don t provides map a means it, to achieve you can t improved manage understanding it. of humanity s relationship to planet Earth. Dmitry Aksenov, Global Forest Watch Russia Gaile and Willmott, Geography in America Many applications implemented using geographic information systems depend on datasets derived from remotely sensed imagery. Aronoff, Remote Sensing for GIS Managers Many more traditional approaches to earth observation (i.e., surface studies) can be limited by too much detail on too few samples or by only having data from a very restricted locale. This is the classic can t see the forest for the trees problem. The synoptic perspective offered by remote sensing lets us look at whole forests, regions, continents, or even the world and yet, at appropriate scales, can let us see not only the whole forest but also the individual trees as well. Schott, Remote Sensing: The Image Chain Approach

14 Earth s s shrinking biosphere land area, ha/capita Important read: Foley et al., 2005 Global Consequences of Land Use

15 Remote Sensing: Permits acquiring unique measurements Offers a synoptic perspective Employs extra-visual information Serves as an historical and permanent record Allows regular data acquisition over vast areas Provides access to remote corners of the world Can be cost-effective Remote Sensing & GIS Remote sensing provides researchers, resource managers, and policy makers with many types of derived data. While GIS provides those same users with a tool for effective storage, manipulation, analysis, synthesis of spatial data for problem solving. Remote sensing is an especially powerful capability when it is incorporated into a geographic information system. These systems integrated satellite and other geophysical data with socioeconomic data such as population demographics. What results are maps that allow researchers to see their parameter of interest in relation to their geographic position. Schmidt Applications Recommended reading: Schmidt, Terra Cognita: Using Earth Observing Systems to Understand Our World

16 History of Remote Sensing Man must rise above the Earth - to the top of the atmosphere and beyond - for only thus will he fully understand the world in which he lives. Socrates, B.C.

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18 Landsat s History L1 launched July 23, 1972 L7 launched Apr. 15, 1999 LDCM ~2011 MODIS & ASTER: Terra launched Dec. 18, 1999 Aqua launched May 4, 2002

19 How does this stuff work? The remote sensing process Remote sensing physics fundamentals Image processing

20 The Remote Sensing Process Aronoff, 2005

21 Remote Sensing Physics Fundamentals Aronoff, 2005 Radiation: the process by which electromagnetic energy is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space Electromagnetic radiation (EMR) acts as both a particle and a wave It needs no transport medium It travels at the speed of light It is described by frequency and wavelength

22 Speed of Light Speed of light ( c): 3 x 10 8 (meters per second) 186, miles per second 1 foot per nanosecond C CCRS

23 Wavelength Wavelength (λ) is defined as the mean distance between the maximums or minimums of a roughly periodic pattern. Normally measured in micrometers (µ) or nanometers (nm).

24 Frequency Frequency (ν or ƒ) is the number of wavelengths that pass a point per unit of time. Frequency is expressed as the number of wave crests per second (one cycle per second is one hertz). Frequency (ν) depends on the number of accelerations per second.

25 Equation for the Speed of Light The speed of light ( c ) is based on the relationship between wavelength (λ) and frequency (ν) of EMR. The formula for c is: c = λν Therefore wavelength and frequency are inversely related So, longer wavelengths have lower frequency, and vice versa

26 Units of Measure Wavelength Meter (m) = 1.0 m Centimeter (cm) = 0.01 m or 10-2 m Millimeter (mm) = m or 10-3 m Micrometer (µm) = or 10-6 m Nanometer (nm) = or 10-9 m Frequency Hertz (Hz) = 1 cycle per second Kilohertz (KHz) = 10 3 or 1 thousand cycles per second Megahertz (MHz) = 10 6 or 1 million cycles per second Gigahertz (GHz) = 10 9 or 1 billion cycles per second

27 Wavelength Exercise Calculate your height in µm 1 foot = m 1 inch = m Vlad Gajic

28 Wavelength & Frequency Exercise Calculate the wavelength of your favorite FM radio station FM frequencies are measured in MHz The speed of light is 3 x 10 8 m/s c = λν

29 Solar EMR & Remote Sensing EMR radiated by atomic particles at the source (sun) Then propagated through the vacuum of space at the speed of light Interacts with the Earth s atmosphere Interacts with the Earth s surface Interacts with the Earth s atmosphere Reaches the remote sensor - where it interacts with various optical systems, filters, film emulsions, or detectors

30 Electromagnetic Spectrum Remote sensing involves measuring (sampling) radiation within the EM spectrum

31 Electromagnetic Spectrum (EMS) World of Beams

32 EMS Regions Important to Remote Sensing Visible light (VIS): µm Blue: µm Green: µm Red: µm Near infrared (also called solar infrared or reflected infrared, NIR): µm Middle infrared (MIR, also called shortwave infrared, SWIR): µm Thermal infrared (TIR): µm and µm Microwave and radio waves (radar): 1mm to 10 m Recall we are limiting our scope to 0.4 µm to 15 µm Aronoff, 2005

33 Visible Spectrum: Color Concepts Very small portion of the EMS ROY G. BIV is back Rossing & Chiaverina, 1999

34 Energy sources Passive vs. active remote sensing For passive there are two energy sources: the sun and emitted radiation Emission - the process by which a body emits electromagnetic radiation as a consequence of its kinetic temperature only Aronoff, 2005

35 Blackbodies Rossing & Chiaverina, 1999 Energy is emitted by all objects above absolute zero Objects typically give off radiation at an infinite number of wavelengths Objects give off more radiation at some wavelengths than others A blackbody gives off radiation at the maximum rate possible at each wavelength and temperature The hotter the blackbody the higher its radiation rate at every positive-valued wavelength & the shorter the wavelength of its peak emission

36 Solar Irradiation Curves Nick Short, NASA

37 Space-based Remote Sensing When the sun s energy passes through the atmosphere, three reactions can occur: Transmission Scattering Absorption Aronoff, 2005

38 Scattering Radiation is scattered by atmospheric particles. In contrast to transmission (and subsequent refraction), the direction of scattering is unpredictable. Three types of scattering: Rayleigh Scattering (a.k.a. molecular scattering) Mie Scattering (a.k.a. non-molecular scattering) Non-selective Scattering

39 Rayleigh Scattering Occurs when the diameter of the matter (air molecules such as oxygen and nitrogen) are many times smaller than the wavelength of incident EMR Varies as a function of the pressure and density of the atmosphere. Most Rayleigh scattering takes place in the upper 4.5 km of the atmosphere. Responsible for the blue sky. Shorter violet and blue wavelengths are more efficiently scattered than the longer wavelengths.

40 Mona?

41 Mie Scattering Involves spherical particles with diameters approximately equal to the size of the wavelength of incident energy. For visible light, dust, smoke, and pollution are the primary Mie scatterers Takes place in the lower 4.5 km of the atmosphere. The amount of scattering is greater with Mie than Rayleigh. Mie scattering contributes to beautiful sunsets. The greater the amount of smoke and dust particles in the atmosphere, the greater the amount of violet and blue light that will be scattered - and only the orange and red wavelengths reach our eyes.

42 Non-Selective Scattering Non-selective scattering takes place in the lowest portion of the atmosphere and involves interaction with particles greater than 10 times the wavelength of the incident radiation (water droplets, ice crystals). It is non-selective because all wavelengths are scattered, not just blue, red, or green. EMR passing through fog or clouds will appear white because all visible wavelengths are scattered equally well.

43 Why Worry About Scattering? Scattering changes the properties of the recorded EMR and reduces the information content in the resulting images. The loss of information is manifested as a loss of contrast and makes it difficult to differentiate from adjacent features.

44 Absorption Absorption is the process by which radiant energy is absorbed and converted to other forms of energy. Absorption takes place both in the atmosphere and on the terrain.

45 Absorption Band Absorption band is a range of wavelengths or frequencies in the EM spectrum within which radiant energy is absorbed by a substance. Common absorbers are water (H 2 0), carbon dioxide (CO 2 ), oxygen (0 2 ), ozone (O 3 ), and nitrous oxide (N 2 0). Certain regions of the electromagnetic spectrum are completely shut down (meaning that EMR is absorbed and cannot pass through) by the cumulative affect of the absorbing constituents.

46 Why are We Concerned About Absorption? Absorption creates information. For example, some features are strong absorbers (water absorbs near infrared, chlorophyll absorbs blue and red light). Absorption cause loss of information. Remote sensing instruments must have bands or channels that are designed to avoid imaging in the absorption bands of the EM spectrum.

47 Atmospheric Windows What spectral windows one is peaking through The regions of the EM spectrum that transmit energy effectively are called Atmospheric Windows. The visible portion of the spectrum (0.4 to 0.7 µm) is an atmospheric window as it transmits all of the incident energy. Aronoff, 2005

48 Energy Received at Satellite Energy reaching Earth-observing satellites (observing 0.4 µm 15 µm of EMS) follows one of two energy paths: (1) Solar energy path: radiation originating from the sun (2) Thermal energy path: radiation resulting from the temperature of objects other thank the sun Aronoff, 2005

49 Solar Energy Path Radiation originating from the sun Schott, 1997 A = sunlight that goes through the atmosphere and bounces back, what let s us see color B = scattered by atmosphere then reflected by Earth (shadow of a building, cloudy days, more type B) C = upwelled radiance, path radiance never hits Earth, haze, air light, flare light G = reflects off more than one object before propagating back to space (in most natural (i.e. rough environments in level terrain; multiple bounce photons do not make a significant contribution) I = bounce and scatter photons, adjacency effect photons (typically can be lumped with type C photons)

50 Thermal Energy Paths Radiation resulting from the temperature of object other than the sun In some portions of the EMS (e.g. 10µm) self-emitted photons become very important D = Photons typically caused by radiation due to temperature of the target itself E = downwelled radiance (like B, but thermal). Selfemitted radiation from atmosphere which has some nonzero temperature F = directly from atmosphere, never make it to Earth (like G) H = radiated energy from a background object which propagate to the ground and then are reflected by ground. Schott, 1997

51 Energy interaction with Target A fundamental aspect of remote sensing is monitoring how incoming (incident) radiant flux in selected wavelengths interacts with the land surface When energy comes into contact with a target it is either: (1) Transmitted - radiation passes through the target (light through a leaf) (2) Absorbed - radiation is absorbed by the target and later emitted as thermal infrared energy (heat) --> thermal energy path (3) Reflected - radiation bounces off of target --> solar energy path

52 Reflectance Reflectance (R, ρ, ρ λ, r λ ) is the process where radiation bounces off an object. A fundamental characteristics of reflectance is that the angle of incidence and the angle of reflection (exitance) are approximately equal. Types of reflectance: Specular - essential smooth surface. The average surface height is several times smaller than the wavelength of radiation striking the surface. Near-perfect specular reflectors: calm water bodies, shiny dark cars Specular reflectance creates a mirror image. Diffuse - Radiation striking the surface is reflected in many directions depending on the orientation of the smaller reflecting surface. This occurs if the surface height is large relative to the size of the wavelength of incident energy. Rough surfaces are diffuse reflectors (field of grass)

53 Types of Reflecting Surfaces Rees, 2001 (a) (b) (c) (d) (e) Specular Quasi-specular Lambertian Lambertian Surface: a perfectly diffuse surface in which the radiant energy leaving the surface is constant for any angle of reflectance Quasi-Lambertian Complex

54 Understanding Reflectance Measurements Percent reflectance (%R) is one of the most common measurements in remote sensing %R is the ratio of outgoing radiant flux to incoming radiant flux (x 100) Radiant flux (Φ): measure of the total power of EMR onto, off of, or through and a surface per unit of time (measured in Watts) Note: radiometric quantities are based on the amount of radiant energy incident to a surface from any angle in a hemisphere (i.e., half of a sphere). Earth Surface %R = r λ x 100 r λ = Φ reflected / Φ incident

55 Radiant Flux Density Radiant Flux Density: The amount of radiant flux per unit area at a point on the surface Two possibilities: (1) radiant flux is arriving: Irradiance (E λ ): The amount of radiant flux incident per unit area of a plane surface, i.e., energy incident on surface (W m -2 ) E λ = Φ λ / Area (2) radiant flux is exiting: Exitance (M λ ): The amount of radiant flux leaving per unit area of a plane surface. (W m -2 ) M λ = Φ λ / Area

56 Radiance Radiance (L λ ): The radiant flux per unit per unit solid angle and per unit projected area of radiating surface. Radiance is expressed as Watts per meter squared per steradian (W m -2 sr -1 ). The radiant flux leaves the projected source area in a specific direction toward the remote sensor.

57 Radiance and Atmosphere Scattering in the atmosphere and from other areas on the ground can cause spurious spectral energy to enter into the solid angle field of view. The combined atmospheric effects due to scattering and absorption are wavelength-dependent. They also vary in time and space, and depend on the surface reflectance and its spatial variation. At-sensor radiance TOA reflectance, at-sensor reflectance Surface reflectance

58 Landsat 7 Corpus Christi Nov. 22, 2002 TOA reflectance

59 Landsat 7 Corpus Christi Nov. 22, 2002 Surface reflectance

60 Atmospheric Corrections Atmospheric correction algorithms involve two major steps: (1) The optical characteristics of the atmosphere are either estimated empirically, atmospheric constituents are directly measured, or they are estimated theoretically by models. The amount of atmospheric correction can then be computed by radiative transfer algorithms, given the atmospheric optical properties. (2) The remotely sensed imagery is corrected by inversion procedures that derive the surface reflectance. Masek et al., 2006

61 Multispectral Remote Sensing: History During WWII, color infrared film was developed Used to discern camouflage from vegetation; vegetation was bright red; camouflage was not!

62 Spectral Signatures» The spectral response of a surface relates to the type and/or condition of surface features» Spectral signature is a term used to refer to spectral response Aronoff, 2005

63 Spectral Signatures The motivation of multispectral remote sensing is that different types of materials can be distinguished on the basis of differences in their spectral signatures. - Schowengerdt, 2005 Spectral location of sensor bands constrained by: atmospheric absorption bands reflectance of features to be measured; i.e., their Spectral Signaures

64 Spectral Signatures» Signatures of common food items Rossing & Chiaverina, 1999

65 Color Signatures Rossing & Chiaverina, 1999

66 Color Exercise What color is represented by each graph? Rossing & Chiavernia, 1999

67 Basic Surface Reflectance Properties Vegetation Visible light is absorbed due to pigments in plant leaves Chlorophyll is a strong absorber of 0.45 and 0.67 µm EMR, and a weak reflector of 0.55 µm EMR. Near IR in the range of 0.7 to 1.3 µm EMR is strongly reflected due to the properties of the internal structure of leaves (spongy mesophyll). Because the internal structure of plant leaves is so variable between species, there are greater differences in NIR reflection. Plant stress affects the plant internal structure, making it possible to identify plant health problems. Canopy density increases NIR reflectance due to retransmittance and reflectance of EMR. In the Short- or Mid-IR region, leaf reflectance is inversely related to the amount of water in the leaf (e.g., reflectance goes up as leaf water content goes down).

68 Basic Surface Reflectance Properties Soil Very little peak-and-valley variability (unlike vegetation). Specific factors that affect soil reflectance include: Moisture content (decreases reflectance) Soil texture (generally, finer texture soils reflect less than coarse texture soils - because of higher moisture content) In the absence of water, coarse textured soils will be less reflective. Surface roughness (rougher surfaces reflect less) Presence of iron oxides (presence of iron oxides reduces reflectance) Organic matter content (higher levels of OM reduces reflectance)

69 Basic Surface Reflectance Properties Water Has very low visible reflectance (0.4 to 0.8 µm). Clear water does not reflect beyond 0.6 µm. Absorbs from NIR and beyond (no reflectance) As turbidity increases, transmittance - and therefore reflectance - increases. However, the detection of turbidity is most likely in the visible region of the spectrum.

70 Using a Spectrometer Vernier ALTA II Reflectance Spectrometer % Reflectance = (Display voltage for sample dark voltage) (Display voltage for standard dark voltage) * 100

71 Collecting Spectra Open ALTA.xls

72 Plot your results (Leaf)

73 Alas, Remote Sensing Caveats Satellite sensors seldom sample pure vegetation, soil, or water reflectance They typically sample areas that integrate reflectance from mixtures of vegetation, soil, or water Spectral signature measurements can be foiled by: spectral variability for a given material coarse quantization* of RS system modification of signatures by the atmosphere Most RS systems only give you a few data points Schowngerdt, 2007

74 An Incomplete Signature Canada Centre for Remote Sensing

75 Mixed Pixels and Spectral Response Percent Reflectance 27.6

76 Broadleaf shrubs Water Grassland Needleleaf Forest

77 Understanding Satellite Sensors Sensor platforms Satellite orbits Types of passive sensors Sensor resolution Data ground transmission

78 Sensor Platforms Platforms: The device holding a remote sensing device. A stable platform holds the sensor that collects and records energy reflected or emitted from a target or surface. Platforms include can be on the ground, on an aircraft or balloon, or on a spacecraft. Rees, 2001

79 Satellite Orbits Orbit - the path followed by the satellite. Satellite orbit characteristics are matched to the mission and objectives of the sensors they carry. Orbits vary according to their altitude (height above the Earth's surface), and their orientation and rotation relative to the Earth. Types of orbits: Equatorial Geosynchronous Polar Polar Sun-synchronous

80 Equatorial Orbits Uncommon for satellite remote sensing. Orbital track generally takes latitudinal tracks about the equator. Difficult to obtain complete global image coverage from equatorial orbits. Examples Space Shuttle Tropical Rainfall Monitoring Mission

81 Geostationary Orbits Geostationary orbits have altitudes of approximately 36,000 km and revolve around the Earth at speeds that match the speed of the Earth s rotation. This synchronization relative to the Earth's surface allows the satellites to observe and collect information continuously over specific areas. Weather and communications satellites commonly have these types of orbits. Due to their high altitude, some geostationary weather satellites can monitor an entire hemisphere of the Earth.

82 Polar Orbits A near north-to-south orbit (pole-to-pole) which, in conjunction with the Earth's west-to-east rotation, allow a satellite and sensor to cover most of the Earth's surface over a certain period of time. In a near-polar orbit, the inclination of the orbit is relative to a line running between (not over) the North and South poles.

83 Sun-Synchronous Polar Orbits Polar orbits are sun-synchronous when they cover each area of the world at a constant local time of day (called local sun time). At any given latitude, the position of the sun in the sky as the satellite passes overhead will be the same within the same season. This type of orbit ensures consistent illumination conditions when acquiring images in a specific season over successive years, or over a particular area over a series of days. This is an important advantage when analyzing images from year to year since the images do not have to be corrected for different illumination conditions. Natural Resources Canada

84 Ascending and Descending Orbit Passes In near-polar orbits, the satellite travels northwards (ascending) on one side of the Earth and then toward the southern pole (descending) on the second half of its orbit. Generally, for sunsynchronous orbits, the ascending pass is on the shadowed side of the Earth while the descending pass is on the sunlit side.

85 Orbital Swaths As a satellite revolves around the Earth, the sensor "sees" a certain portion of the Earth's surface. Since the Earth rotates, a different area is imaged every orbit. The area imaged on the surface, is referred to as the swath. Image swath widths for spaceborne sensors are altitude and instrumentspecific, but generally vary between tens to thousands of km wide. Wider swaths mean less time needed for complete global coverage (i.e., shorter repeat cycle). Aronoff, 2005 CCRS

86 Orbit Cycles, Nadir, and Revisits The point directly below the satellite (a plumb line) is the nadir point. For any pass in a satellite's orbit, an orbit cycle will be completed when the satellite retraces its path, passing over the same nadir point for a second time. Revisit period: The frequency that the same area can potentially be imaged. Using pointable sensors, an satellite-borne instrument can view an area (off-nadir) before and after the orbit passes over a target, thus making the 'revisit' time less than the orbit cycle time.

87 Overlap and Convergence In near-polar orbits, areas at high latitudes will be imaged more frequently than the equatorial zone due to the increasing overlap in adjacent swaths as the orbit paths come closer together near the poles.

88 Types of Sensors: Electromagnetic Scanners Scanning systems employ a sensor with a narrow field of view (i.e. IFOV) that sweeps over the terrain to build up and produce a two-dimensional image of the surface. A scanning system used to collect data over a variety of different wavelength ranges is called a multispectral scanner (MSS), and is the most commonly used scanning system.

89 Electromagnetic Scanners There are two main modes or methods of scanning employed to acquire multispectral image data: Across-track scanning (a.k.a. whiskbroom, electro-optical, or electro-mechanical) Along-track scanning (a.k.a. push-broom)

90 Across-Track Scanners Across-track scanners scan the Earth in a series of lines. The lines are oriented perpendicular to the direction of motion of the sensor platform (i.e. across the swath). A bank of internal detectors, each sensitive to a specific range of wavelengths, detects and measures the energy for each spectral band and then, as an electrical signal, they are converted to digital data and recorded for subsequent computer processing. The IFOV of the sensor and the altitude of the platform determine the ground resolution cell (the spatial resolution). The angular field of view is the sweep of the mirror used to record a scan line (measured in degrees), and determines the width of the imaged swath. Aronoff, 2005

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92 Along-Track Scanners Along-track scanners also use the forward motion of the platform to record successive scan lines and build up a two-dimensional image, perpendicular to the flight direction. Instead of a scanning mirror, they use a linear array of detectors located at the focal plane of the image formed by lens systems, which are "pushed" along in the flight track direction (i.e. along track). A separate linear array is required to measure each spectral band or channel. For each scan line, the energy detected by each detector of each linear array is sampled electronically and digitally recorded. Aronoff, 2005

93 Aronoff, 2005

94 Resolution Spectral Spatial Temporal Radiometric Describing remotely sensed imagery

95 Spectral Resolution

96 Spectral Resolution

97 Spectral Resolution Band, Channel, Regions: Arbitrary, sensorspecific terms for the wavelength interval (defined by the lower and upper wavelength). Spectral resolution is described in terms of bands of the EM spectrum.

98 Landsat 7, Path 35 Row 34, ,2,1

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102 SpatialResolution Richard Irish, NASA

103 SpatialResolution Laura Rocchio, NASA

104 IFOV IFOV = Instantaneous field of view IFOV determines the ground area sensed by the sensor at a given instant IFOV therefore determines the ground resolution element or resolution cell The resolution area is expressed as a circle of diameter D: D = H β Where D = diameter of the circular ground area viewed H = altitude of sensor β = IFOV of the system (in radians) Aronoff, 2005

105 IFOV Exercise The ASD field spectrometer we used last year has an 18º IFOV If you hold the sensor 1 meter above the ground, what is the diameter of the ground resolution cell? D = H β Recall, 1º = Π/180 radians So, 18º = 18 Π/180 radians And, 18º = Π/10 ASD

106 Temporal Resolution The revisit time of the satellite over a given point on the ground Landsats 4, 5, and 7 all have/had a 16 day repeat cycle Landsat 1, 2, and 3 had an 18 day repeat cycle Landsat 5 and 7 eight days apart, (see on Glovis)

107 Radiometric Resolution Radiometric Resolution: The sensitivity of a sensor and image to the magnitude of the electromagnetic energy The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in reflected or emitted

108 Radiometric Resolution Image data are represented by positive digital numbers which vary from 0 to (one less than) a selected power of 2. This range corresponds to the number of bits used for coding numbers in binary format 12 bits = 2 12 = 4096 values 8 bits = 2 8 = 256 values 7 bits = 2 7 = 128 values This range of values (or shades of grey), describes the dynamic rage of an image. The process of converting at-sensor radiance to a digital number (i.e., 0 to 2 n -1) is known as quantization

109 Radiometric Resolution 2 bit image 8 bit image

110 Landsat Resolution Landsat 5 and 7 have a 16-day repeat cycle (they are 8 days out of phase with each other) Data is quantized to 8 bits (256 shades of grey)

111 ASTER Resolutions» Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) has a 60 km swath and 14 channels (3 VIS - 15m, 6 SWIR - 30m, 5 TIR - 90m)» Radiometric resolution = 8-bit» Temporal resolution = pointable, VIS = 24º, SWIR & TIR = 8.54º, only collects on demand ASTER, May 10, 2000 Palm Springs, CA

112 MODIS Resolutions Moderate Resolution Spectroradiometer (MODIS) acquires neardaily global data at 3 resolutions: 250 m (2 bands) 500 m (5 bands) 1000 m (29 bands) All spectral data are calibrated and quantized at 12 bits (4096 digital numbers) MODIS 250 m & 500 m Band Wavelength (μm) Descrip Red Near IR Blue Green Mid IR Mid IR Mid IR *MODIS data products

113 TERRA MODIS November 29, 2003

114 Resolution Trade Offs No sensor is an island Engineers must make trade-offs between spatial spectral, radiometric, and temporal resolutions High spatial resolution requires a small IFOV Small IFOV reduces the amount of energy that can be detected since the ground resolution cell is smaller This means the ability to detect small amounts of energy is reduced (radiometric resolution) To increase energy, the spectral band can be broadened, but this means a loss of spectral resolution For polar sun-synchronous satellites, high temporal resolution necessitates a wide swath Typically, a wider swath means lower spatial resolution The longer the wavelength, the lower the energy content. Longer wavelength images tend to have lower spatial resolution

115 Data Transmission Data collected by a satellite is downlinked to a ground station The data is processed, archived, and made available to you!