This document discusses different types of sensors used in remote sensing. Passive sensors detect electromagnetic radiation emitted or reflected from the object of interest, while active sensors emit their own radiation and measure the return signal. Examples of passive sensors mentioned are AVHRR for sea surface temperature and SeaWiFS for ocean color. Microwave and infrared radiometers are also passive sensors. Active sensors include altimeters, scatterometers, and synthetic aperture radars. The document provides examples of applications of remote sensing such as agriculture, cartography, engineering, geology, and oceanography.

1. 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.

2. Examples of Passive Sensors
 Advanced Very High Resolution Radiometer
(AVHRR)- Sea Surface Temperature
 Sea-viewing Wide Field-of-View Sensor
(SeaWiFS)- Ocean Color

3. 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.

4. Advantages of passive microwave remoteAdvantages 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

5. 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.

6. IoE 184 - The Basics of Satellite Oceanography. 1. Satellites and Sensors
Sensors on satellites
Passive sensors Wavelength Information
Visible wavelength
radiometers
400 nm - 1 µm Solar radiation reflected
by Earth surface
Infrared (IR) radiometers about 10 µm 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

7. 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.

8. 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.

9. 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.

11. 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); and
In 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.

12. 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

13. Remote sensing applications
Cartography
map revision
geodesy and photogrammetry
merging other data with remote sensing
for map presentation
use of stereo imagery for topographic
mapping
compile and update thematic maps of
various resources

14. Remote sensing applications
Engineering
routing power lines
designing transportation networks
site selection

15. Remote sensing applications
Erosion mapping
mapping and monitoring eroded areas
predicting potential erosion sites
monitoring land degradation and
desertification

16. 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

17. Remote sensing applications
Hydrology
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

18. 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

19. 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

20. 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

21. 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

22. Remote sensing applications
Urban studies
mapping extent of, and changes, in urban
settlements
studies of housing density and urban drainage
land use planning