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Remote Sensing Outline: definition of remote sensing components of system electromagnetic radiation nature of an image light interaction with atmosphere and surface types of remote sensors Remote Sensing science and art of obtaining information about something from a distance. analysis of collected data to obtain information about the objects, areas or phenomenon under investigation. Components of System propagation through the atmosphere energy interactions with earth surface features transmission through the atmosphere Components of System Data Analysis: examining the data using various viewing and interpretation devices to analyze pictorial data and/or a computer to analyze digital sensor data (i.e. GIS). Electromagnetic Radiation Energy Sources: energy available from sun is described by electromagnetic spectrum Electromagnetic Radiation Wavelength - distance from one wave crest to another. Frequency - number of wave crests passing a fixed point in a given period of time. Measured in hertz (1 cycle per second) Electromagnetic Radiation Amplitude - height of each peak. Measured as spectral irradiance Electromagnetic Radiation Ultraviolet Radiation - 0.4 micrometers not much is done with UV for remote sensing since these shorter wavelengths are easily scattered by the atmosphere Electromagnetic Radiation Visible Radiation BLUE (.4-.5 micrometers) GREEN (.5-.6 micrometers) RED (.6-.73 micrometers) Electromagnetic Radiation Infrared Radiation - .72 - 15 micrometers 1. Near Infrared - reflected, can be recorded on film 2. Mid Infrared - reflected, can be detected using electro-optical sensors. 3. Thermal Infrared emitted, can only be detected using electrooptical sensors Electromagnetic Radiation Microwave Radiation - radar sensors, wavelengths range from 1mm to 1m Electromagnetic Radiation most systems rely on the sun to generate all the EM energy needed to image terrestrial surfaces - passive sensors. other sensors generate their own energy, called active sensors, transmits that energy in a certain direction and records the portion reflected back by features within the signal path Light Interaction with Atmosphere atmospheric modification of incoming and outgoing EM radiation includes scattering, refraction and absorption Scattering redirection of light by particles can be in any direction Light Interaction with Atmosphere General Effects of Scattering causes skylight (allows us to see in shadow) forces image to record the brightness of the atmosphere in addition to the target. directs reflected light away from the sensor, decreasing spatial detail (fuzzy images) tends to make dark objects lighter and light objects darker (reduces contrast) Light Interaction with Atmosphere Refraction bending of light when it passes through two media degrades spectral signatures on hot- humid days Light Interaction with Atmosphere Absorption mostly caused by three atmospheric gases: ozone, carbon dioxide and water vapour no attenuation attenuation Light Interaction with Surface Reflection the bouncing of electromagnetic energy from a surface type of reflection is dependent on the size of the surface irregularities relative to the incident wavelength. Light Interaction with Surface 1. Specular Reflectance light is reflected in a single direction - 'mirror' reflection specular reflectance helps and hinders remote sensing Light Interaction with Surface 2. Diffuse/Lambertian Reflectance energy is reflected equally in all directions many natural surfaces act as a diffuse reflector to some extent. Nature of the Image image – model target features described through the use of spectral reflectance software and hardware specially designed to analyze these images give us the ability to see a pictorial rendition of targets. images that we see on a computer screen are made up of picture elements called pixels. Nature of the image Pixel - picture element having both spatial and spectral properties. the spatial property defines the "on ground" height and width. the spectral property defines the intensity of spectral response for a cell in a particular band Nature of the Image Nature of the Image when only one band of the EM spectrum is sensed, the output device (colour monitor) renders the pixels in shades of grey Nature of the Image multispectral sensors detect light reflectance in more than one or two bands of the EM spectrum. these bands represent different data - when combined into the red, green, blue guns of a color monitor, they form different colors Nature of the Image multispectral image is composed of 'n' rows and 'n' columns of pixels in each of three or more spectral bands Aerial Photography/Airphoto most common, versatile and economic form of remote sensing spectral range 0.3 to 0.9 mm (visible portion of spectrum). photogrammetry is the science, art and technology of obtaining reliable measurements, maps, other derived products from photographs. ADVANTAGES OF AERIAL PHOTOGRAPHY Five Basic Advantages Improved vantage point Capability to stop action Permanent recording Broadened spectral sensitivity Increased spatial resolution and geometric fidelity Aerial Photography/Airphoto camera produces a large-format 23x23cm photo contain high precision/well calibrated lenses that minimize spatial distortions motor-driven film advances – 60% overlap between successive exposures panchromatic, black-and-white, true-colour film Aerial Photography/Airphoto Grey scale step wedge Notes Altimeter Fiducial marks Clock Lens serial number Focal length Frame number Mission name and date Aerial Photography/Airphoto Airphoto – Saudi Arabia Aerial Photography/Airphoto advantages: improves vantage point, capability to stop action, permanent recording, broadened spectral sensitivity, increased spatial resolution. disadvantages: can’t get at elevation, not appropriate for urban areas (tall buildings block information) applications: land use/land cover mapping, geologic and soil mapping, agricultural application, forest applications, wildlife ecology, etc. Satellite Remote Sensors currently there are 2777 satellites orbiting the earth (US – 878) multi-purpose: scientific defense communications global positioning system (GPS) Satellite Remote Sensors geostationary orbiting satellites are those that remain stationary relative to a point on the surface of the earth i.e. communications and meteorological satellites Satellite Remote Sensors polar-orbiting satellites are those in which the position of the satellite’s orbital plane is kept constant relative to the sun. i.e. Landsat satellite series ACTIVE VS PASSIVE REMOTE SENSING Passive Remote Sensing measure natural radiation emitted by target or/and radiation energy from other sources reflected from the target examples: passive microwave radiometers, LandSat, SPOT ACTIVE VS PASSIVE REMOTE SENSING Active Remote Sensing transmit their own signal and measure the energy that is reflected or scattered back from the target advantages: ability to “see” regardless of time of day or season; use wavelengths not part of solar spectrum; better control of the way target is illuminated Microwave Sensors sensors that operate in the microwave portion of the spectrum advantages: capable of penetrating atmosphere under disadvantage: radar instruments have a hard time applications: sea ice and snow, geologic features, ocean virtually all conditions, different view of the environment. identifying water bodies because the wavelength is much longer than the general character of the surface roughness bottom contours, other planets. Microwave Sensors Microwave radiometer – narrow-beam antenna attached to a scanning device soil moisture, water content of snow, geologic strata Synthetic Aperture Radar – shorter antenna that emits and receives returned energy from ground objects day/night, clouds/cloud free operation Microwave Sensors RADARSAT launched in November 1995 developed by Canada to monitor environmental change and the planet’s natural resources heart is synthetic aperture radar (SAR) – microwave instrument that sends pulsed signals to earth and processes the received reflected pulses. Microwave Sensors First RADARSAT Image Microwave Sensors European SAR ERS-2 Vancouver Island Optical Sensors sensors that operate in the optical portion of spectrum, which extends from approximately 0.3 to 14 mm. can do more with these data because it is numbers. look at differences in colors look at differences over time applications: meteorological, ocean monitoring (i.e. chlorophyll absorption). Optical Sensors show how much energy from the sun was being reflected or emitted off the Earth's surface when the image was taken. clear water reflects little radiation, so it looks black. pavement and bare ground reflect a lot of radiation, so they look bright. urban areas usually look light blue-grey. vegetation absorbs visible light but reflects infrared, so it looks red Optical image of Montreal area during ice storm of 1998. Ice snow and clouds appear as various colors of white, vegetation is green. Optical Sensors GOES - Geostationary Operational Environmental Satellite (Visible to NIR, Thermal) DMSP - Defense Meterological Satellite Program 600 m resolution (Visible to NIR, Thermal), urban heat island studies Nimbus - CZCS - coastal zone color scanner, 825 m spatial resolution AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal) AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal) AVHRR Channels Channel 1 2 Wavelength 0.58 - 0.68 0.725 - 1.10 3A 3 1.58 - 1.64 3.55 - 3.93 4 10.30 - 11.30 5 11.50 - 12.50 Primary Use Daytime cloud/surface mapping Surface water delineation, ice and snow melt Snow / ice discrimination (NOAA K,L,M) Sea surface temperature, nighttime cloud mapping Sea surface temperature, day and night cloud mapping Sea surface temperature, day and night cloud mapping Optical Sensors LANDSAT - visible, NIR spectral bands (Landsats 1,2,3), and MIR and Thermal (Landsats 4 and 5) Multispectral scanner - 4 spectral bands – Green, Red, and 2 NIR Thematic mapper - 7 spectral bands – Blue/Green, Green, Red, NIR, MIR, MIR, Thermal LANDSAT MSS image - Grand Canyon LANDSAT TM image - southwestern Utah and Southern Nevada SPOT Image of the WTC Fires