2. Remote Sensing

7. Remote Sensing requires the following:
1. Electromagnetic Energy Source
2. Interaction with a Target
3. Sensor to Record Energy
4. Transmission, Reception and Processing
5. Interpretation
6. Application
Electromagnetic Energy Source
Illuminates or provides electromagnetic radiation to the
target of interest

8. A - Source of
Electromagnetic
Radiation
B - Radiation comes
into Contact
with Atmosphere
C - Radiation
Interacts with
Target
D - Sensor Collects and
Records Electromagnetic
Radiation
F - Processed Image
Interpreted to
Extract Target Info
E - Recorded Energy Transmitted
to Processing Station (for copy)
G - Application

9. Radiation Interacts with Atmosphere
Radiation interacts with the atmosphere on the way to the
target and as the energy travels from the target to the sensor
Interaction with a Target
Radiation interacts with target. The nature of this interaction
is dependent on the wavelength of the radiation and the nature of
the target
Sensor
A sensor (mounted on satellite/plane/helicopter) collects/records
the electromagnetic radiation scattered or emitted by the target
Transmission and Processing
Recorded energy is transmitted to a processing station to produce
an image saved in digital format (or hardcopy)

10. * Remote sensing is especially important for
Interpretation
Visual interpretation or digital (GIS) interpretation to extract
further information about the target
Application
Information applied to solve a problem
* Remote sensing is especially important for
extracting information from harsh environments
or difficult terrain

14. Passive Sensors
Measure naturally-available energy
(eg. thermal infrared radiation
emitted from the Earth 24 hours
per day, but solar reflected
radiation only during solar day)
Active Sensors
Sensor emits radiation toward target
Reflected radiation in emitted bands
are detected and measured
(eg. microwaves emitted)

21. Characteristic spectral responses of different surface types
Characteristic spectral responses of different surface types. Bands are those
of the SPOT remote sensing satellite.

24. Images and Photographs
Representation in digital format
by subdividing image into equally-
shaped areas called pixels
The ‘brightness’ of
each area can be
attributed a numeric
value or digital
number
Information from
narrow wavelength
ranges can be stored
in channels, also
called bands
Often, data from multiple channels can be
represented as one of three primary colours
which combine according to brightness.
We are, thus, no longer blind to these ’s.

25. Orbits and Swaths Geostationary orbits:
Very high altitude satellites (approximately km)
Focus on the same area of the Earth at all times
Continual data collection over a specific area
Eg. Weather and communications satellites
Near-polar orbits
Satellite travels northward on one side of the Earth and then
southwards during the second half of its orbit
In sun-synchronous orbits, ascending path can be on a shadowed
side with the descending path on the sunlit side. Passive sensors
would only record data during the descent.

26. Swath
The area imaged on the surface.
Swaths vary from very small areas (helicopters and planes) to
hundreds of kilometres (spaceborne satellites)
Earth rotates: Satellite swath may cover new area with each pass
Complete coverage of Earth after one cycle of orbits
Areas at high latitude generally covered more frequently
Spatial Resolution
Size of the smallest possible
feature that can be detected
Instantaneous Field of View (IFOV)
is the angular cone of visibility of
the sensor (See A at right)
This, along with altitude (C), determines
the area visible on the ground (B)

27. Examples of Remote Sensing Satellites
Each has multiple channels for specific purposes
1. Weather
GOES (Geostationary Operational Environmental Satellite)
NOAA AVHRR (Advanced Very High Resolution Radiometer)
2. Land Surface Observation
Landsat (NOAA)
SPOT (Système Pour l’Observation de la Terre)
IRS (Indian Remote Sensing)
MEIS-II and CASI (Airborne Sensors)
3. Marine Observation
CZCS (Coastal Zone Colour Scanner)
MOS (Marine Observation Satellite)
SeaWiFS (Sea-viewing Wide Field of View Sensor)

28. Applications of Remote Sensing
There are many applications of remote sensing, most of which are
related to Geography as a discipline
Agriculture: Crop type, condition and yield, soil characteristics
Forestry: Type, health, biomass, burning, species, deforestation
Hydrology: Sea ice, navigation, oil spills, sea surface temperature
Land Use: Resource management, habitat protection, urban
sprawl, damage assessment, legal boundaries
Oceans: Currents, winds, waves, phytoplankton concentration,
temperature monitoring, navigation routing, traffic
density, bathymetry, land-water interface delineation,
coastal vegetation
Mapping: Digital Elevation Models (DEM’s), thematic mapping

29. AVHRR Visible, NIR, Thermal
1.1 km Resolution - local area coverage (LAC)
4 km Resolution - global area coverage (GAC)
Used for meteorological studies
Vegetation pattern analysis
Global modeling
Broad spectral bands

30. LANDSAT Thematic Mapper
Sun-synchronous, near-polar orbit, imaging the same 185 km x km ground swath every 16 days
Global coverage between 81 degrees north latitude and 81 degrees south latitude
Particularly useful in determining land use classes
Blue/Green, Green, Red, NIR, MIR, Thermal
30 meter resolution 256 brightness values 7 spectral bands

31. Normalized Difference Vegetative Index (NDVI)
NDVI = (NIR - red) / (NIR + red)

32. RADAR - Radio Detection and Ranging
Passive Microwave Sensors:
Applications include meteorology (atmosphere profiles, water and
ozone content), hydrology (soil moisture) and oceanography (sea
ice, currents, oil slicks)
Active Microwave Sensors:
RADAR - Sensor transmits a microwave (or radio) signal toward a
target and detects the backscattered portion of the signal
Strength of backscattered signal discriminates between targets
Time delay between transmitted and reflected signals determines
the distance to the target
Non-Imaging (eg. altimeters) or Imaging Sensors
Imaging Microwave Sensors include RADARSAT (Canada, 1995)
RADARSAT, developed by the Canadian Space Agency, is the
world’s first, operationally-oriented radar satellite system capable of
rapid delivery of large quantities of data

33. Image Processing
1. Preprocessing
Radiometric and geometric corrections
2. Image Enhancement
Improving contrast, and spatial filtering to enhance specific
spatial patterns of interest
3. Image Transformations
Combined processing of multiple spectral bands for image
enhancement
4. Image Classification and Analysis
Digital identification and classification of pixels.
Classification: Assigns each pixel to a particular class or
theme based on desired statistical characteristics
(supervised or unsupervised)

35. Before GIS: Popularity of stack maps Limitation: Restricted to
consistent scale,
projection and
coverage area

36. Advantage of Digital Overlay:
1. Faster
2. Scale, projection and coverage area
less problematic (Most applications consist of sources collected by different methods and at different scales)
3. Time and error associated with manual integration and redrafting eliminated
Raster or Vector Implementation

37. Raster
Implementation of
Overlay

38. Overview of Overlay Analysis
1. Three maps represented with a common grid
2. Binary maps converted with Boolean operators such as AND and OR
Eg. Suitability Analysis
AND = more than one condition must occur simultaneously
OR = identifies areas with either condition met

40. Boolean Logic in Raster Overlay RECLASS OVERLAY It is often useful
to RECLASS
your data before
performing
OVERLAY

41. Task: Given vegetation map and elevation map, isolate a vegetation type within a particular altitude range
Map 1: Vegetation Map
(VEGMAP)
Map 2: Digital Elevation Model
(DEM1)

42. This requires the use of the AND operation
STEP 1:
Our vegetation of interest is class 6.
Reclass to assign a value of 1 for all values from 6 to just less than 7. All other values are assigned a value of zero.
CLASS6

43. STEP 2:
Use the Digital Elevation Model to isolate the elevations
between 1700 and 1800 m.a.s.l. In the same way, assign a value of
1 to all values from 1700 to just less than 1801 by using a reclass
function.
DEM1718

44. Where do the two isolated characteristics coincide ? Use OVERLAY
Multiply file CLASS6 by DEM1718 to produce the output map
RESULT.
Only pixels with a value of 1 survive to be represented in the output file.
RESULT

45. OVERLAY is often used in combination with other
operations such as near-neighbour operations
Eg. Produce a map of riparian vegetation cover within
100 metres of rivers and streams
Locate buffer zone
100m from rivers
Overlay with
vegetation map
Produce resultant
map of riparian cover

46. Vector Implementation of Overlay
Produces many new polygons due to overlapping
Each new polygon has a unique, new identifier
The identifier is linked to an attribute table
Result is a single layer coverage linked to all attributes