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GCE Kannur
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Two Generic Types of Sensors
A "passive" system generally consists of an array of small sensors or detectors which record the amount of electro-magnetic radiation reflected and/or emitted from the Earth's surface.
An "active" system propagates its own electro-magnetic radiation and measures the intensity of the return signal.
Examples of Passive Sensors
Advanced Very High Resolution Radiometer (AVHRR)- Sea Surface Temperature
Sea-viewing Wide Field-of-View Sensor (SeaWiFS)- Ocean Color
Why Sea-Surface-Temperature?
Sea surface temperature (SST) is a key parameter for energy transfer between the oceans and the atmosphere and AVHRR-derived SST can deliver important data to meteorological and climatological models.
AVHRR imagery is also useful for meteorological applications (for example, providing detailed imagery of cloud systems), and land applications such as vegetation mapping and monitoring.
Advantages of passive microwave remote Advantages of passive microwave remote sensingsensing
• Sees through clouds at lower frequencies• Long heritage, various instruments since 1978• Emissivity sensitive to state of surface, particularly
moisture– Soil moisture
– Snow-water equivalent
– (water is ~80× as absorptive as ice at these frequencies, whereas in visible through infrared, water and ice have similar absorption coefficients)
• But, because of small amount of energy emitted, pixel size must be large
ACTIVE SENSORS (Detect the reflected or emitted
electromagnetic radiation from natural sources.)
PASSIVE SENSORS (Detect reflected responses from objects that
are irradiated from artificially-generated energy sources such as radar.)
Passive
Non-Scanning
Non-Imaging. (They are a type of profile recorder, ex. Microwave Radiometer. Magnetic sensor. Gravimeter. Fourier Spectrometer.
Imaging. (Example of this are the cameras which can be: Monochrome, Natural Colour, Infrared etc.)
Scanning
Imaging. Image Plane scanning .Ex. TV Camera Solid scanner.
Object Plane scanning. Ex. Optical Mechanical Scanner Microwave radiometer.
Active
Non-Scanning
Non-Imaging. (They are a type of profile recorder, ex. Microwave Radiometer. Microwave Altimeter. Laser Water Depth Meter. Laser Distance Meter. Scanning
Imaging. (It is a radar ex. Object Plane scanning:
Real Aperture Radar.
Synthetic Aperture Radar.
Image Plane Scanning:
Passive Phased Array Radar.
IoE 184 - The Basics of Satellite Oceanography. 1. Satellites and Sensors
Sensors on satellites
Passive sensors Wavelength
Information
Visible wavelength radiometers
400 nm - 1 m Solar radiation reflected by Earth surface
Infrared (IR) radiometers about 10 m Thermal emission of the Earth
Microwave radiometers 1.5 - 300 mm Thermal emission of the Earth in the microwave
Active devices
Altimeters 3 - 30 GHz Earth surface topography
Scatterometers 3 - 30 GHz Sea surface roughness
Synthetic aperture radars
3 - 30 GHz Sea surface roughness and movement
Microwave Remote Sensing: Principles and Applications. Advantages
Day/night coverage. All weather except
during periods of heavy rain.
Complementary information to that in optical and IR regions.
Disadvantages Data are difficult to
interpret. Coarse resolution
except for SAR.
Infrared Satellite Imagery These images were obtained with an AVHRR sensor (Advanced
Very High Resolution Radiometer) carried on a NOAA Polar Orbiting Environmental Satellite (POES).
Measures the amount of thermal infrared radiation given off by the surface of the ocean.
The amount of thermal infrared radiation given off by an object is related to its temperature (dying embers give off less radiation than a hot fire and a person gives off even less).
Thus by measuring the amount of radiation given off by the ocean we can calculate its temperature.
Infrared Satellite Imagery These images were obtained with an AVHRR sensor (Advanced
Very High Resolution Radiometer) carried on a NOAA Polar Orbiting Environmental Satellite (POES).
Measures the amount of thermal infrared radiation given off by the surface of the ocean.
The amount of thermal infrared radiation given off by an object is related to its temperature (dying embers give off less radiation than a hot fire and a person gives off even less).
Thus by measuring the amount of radiation given off by the ocean we can calculate its temperature.
Role of space measurements of the earth's topography.
This information has wide applications: in geology (e.g., correlating with plate tectonics effects);
In geophysics (eg., Distribution of is static imbalances); In climatology (e.g., Orographic barriers),In hydrology (e.g., Drainage basin characteristics);In glaciology (e.g., Ice sheet thicknesses); In ecology (e.g., Ecozone disposition); andIn planetology (e.g., Comparative global hypsometry [frequency distribution of elevations]).
High resolution regional coverage (on order of 100 m horizontal and 1 m vertical) is technically achievable even now.
Remote sensing applications
Agriculture
Mapping crop area
Identifying diseases and crop stress
Estimating crop yield in conjunction
with models
Detecting weeds and illicit crops
pasture management
Remote sensing applicationsCartography
map revisiongeodesy and photogrammetrymerging other data with remote sensing for map presentationuse of stereo imagery for topographic mappingcompile and update thematic maps of various resources
Remote sensing applications
Engineering
routing power lines
designing transportation networks
site selection
Remote sensing applications
Erosion mapping mapping and monitoring eroded areas
predicting potential erosion sites
monitoring land degradation and desertification
Remote sensing applications
Geology
Identifying lineaments and other structural features
mapping geomorphology and geobotany
mineral and petroleum exploration
analysing landform and drainage
identifying rock types
identifying oil seepage
access planning and base map preparation
Remote sensing applicationsHydrology
detecting near-surface aquifers for ground water
storage
monitoring irrigation performance and usage
supplement investigations for flood plain
management
monitoring on-farm water storage
mapping current and potential salinity sites
estimating soil moisture and surface temperature
planning engineering constructions and monitoring
their effectiveness
Remote sensing applications
Meteorology routine atmospheric studies of temperature and weather patterns
mapping cloud cover, patterns, composition and temperature
weather forecasting
flood prediction and monitoring
storm warning and damage assessment
locating and tracking cyclones
monitoring bushfires
mapping snow cover, run-off and melt rate
detecting chemical and/or particulate composition of the atmosphere
climate studies
vertical temperature and humidity profiling
deducing geopotential height and upper level wind velocity
mapping cloud drift winds
Remote sensing applications
Oceanography
estimating sea surface temperature
ocean colour mapping
mapping of sea surface and sea floor topography
detecting navigational hazards
mapping ocean currents, wind and wave action
detecting oil spills, thermal effluent or other pollution
mapping fish populations and movements
identifying upwelling areas of biological significance
studies of sea ice and glacial movement
Remote sensing applications
Renewable resources
land cover inventory and monitoring
modeling vegetation structure
detecting land use changes
mapping landform types
mapping potential bushfire status
assessing the impact of natural disasters such
as fire or drought
Remote sensing applications
Shallow water mapping
bathymetric studies
mapping turbidity and estimating suspended sediment
concentration
mapping chlorophyll content, such as for algal
blooms
mapping reef type and morphology
monitoring sea grass distribution
Remote sensing applications
Urban studies
mapping extent of, and changes, in urban settlements
studies of housing density and urban drainage
land use planning
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