Remote Sensing 

            Is the science of acquiring, processing and interpreting images that record the interaction between Electromagnetic energy & matter or RS is the science of acquiring information about the Earth's surface without actually being in contact with it.  Observed object size, shape and character without direct contact with them.

Process of Remote Sensing

Energy Source or Illumination - Illuminates or provides electromagnetic energy to the target of interest.

Radiation and the Atmosphere – The energy travels to target and it will come in contact with target to the sensor.

Interaction with the Target – Energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.

Recording of Energy by the Sensor - after the energy emitted from the target, sensor to collect and record the EM radiation.

Transmission, Reception, and Processing – The energy transmitted from electronic form, to a receiving and processing station where the data are processed into an image.

Interpretation and Analysis – The processed image is interpreted, to extract information about the target which was illuminated.

Application – Apply the information we have been able to extract from the imagery about the target in order to better understand it.

Fields of Application

Meteorology    - Weather forecast,Climate Studies,Global Change

Hydrology       -Water balance,Energy balance,Agrohydrology

Soil Science    - Land evaluation,Soil Mapping

Biology/Nature Conservation-Vegetation mapping/monitoring,Vegetation condition assessment

Forestry         -Forest mapping,de-/re-forestation,forest fire detection

Environmental studies     -pollution,(Ground) water quality,Climate Change

Agriculture Engineering   -Landuse development,Erosion assessment,Water management

Physical Planning            -Physical Planning,Scenario studies

Land Surveying              -Topography (DTM),Spatial Data Models,GIS

Advantages of remote sensing

• Enables to observe a broad area at a time.

• Enables to observe the area for a long period.

• Enables us to know the condition without visiting the area.

• Enables us to know invisible information.

Type of RS: -

Visible and reflective IR RS- The sun reflectance: Optical energy Visible Reflectance, Near Infrared Reflectance, Thermal Infrared Thermal Radiation

(Drown the diagram- source – sensor)

Thermal RS – Object thermal radiation emissivity, temp: Optical energy Visible Reflectance, Near Infrared Reflectance, Thermal Infrared Thermal Radiation

(Drown the diagram – sensor)

Microwave RS – Microwave radiation/ radar backscatter coefficient: Object Microwave - Microwave Radiation.

Spatial Data Acquisition

Collection

Processing

Analysis

Need for spatial data

Urban planer

Engineer

Landuse planner

Data acquisition

- Ground based method (Surveying & mapping, Photogrammetric)

- Remote sensing methods (Field observation by performing land surveying)

Classification of Sensors

A sensor that measures and records electromagnetic energy. Sensors can be divided into two groups

– Passive Sensors: Depend on an external source like Sun, For all reflected energy, this can only take place during the time when the sun is illuminating the earth.

– Active Sensors: Active sensors have their own source of energy. Active sensors include the laser altimeter and radar.

Advantages for active sensors:

– The ability to obtain measurement anytime. Regardless of the time of the day, season or weather.

– Examine wavelengths that are not sufficiently provided by the Sun.

– To better control the way that a target is illuminated.

Platforms:

There are three types of flatforms in RS. These sensing is from 1m to 36,000km height.

- Ground based- Surveying & mapping, Photogrammetry, ground observation

– Airborne : Observations are carried out using aircraft with special modification to carry sensors. It is above 100m  to 40 km height. This system can collect information any time from the earth surface.

– Spaceborne : This is base on satellites system, Satellites are positioned in orbits between 150 – 36,000 km altitude. Due to repetitive coverage of the Earth surface on a continuing basis. 

Remote Sensing Platforms

Platform Altitude(km)

• Geostationary Sat. 36,000

• Earth Observation sat. 400 – 1000

• Space shuttle 240 – 350

• Airplane 0.3 – 7.5

Scanner

It is a one line, or row, in a raster scanning pattern, such as a line of video on a CRT display of a television. Raster data may need to be analyzed at the level of scan lines in order to convert between formats. This radiation level called digital numbers mulitispectral scanners(MSS), have range of 0.3 to 14um. Two type of scanners, pushbroom scanners- Along track scanners, Wishbroom scanners – Across track scanner.

pushbroom scanners- Linear array CCD,Each pixel has its own detector, recording one entire line at the time

Wishbroom scanners- Combination of singal detectors and rotating mirror across track scanner

Benefits med resolution sat in urban area- 

Scope :  Vass area maps can be prepared. Specially vegetation, soil map land use map, forestry maps etc.

Benefits: As this is law resolution images, the primary cost will be less. As there is not much data, we can reduce processing coast.

Swath-

When the satallte move around the earth in obrbit, it sees the portion of earth surface. This image referred as swath

Electromagnetic Radiation

Electromgnetic radiation consist with electrical field(E) and magnetic field(M). RS required energy source to illuminate the target. The two characteristics of EM radiation is wavelength and frequency. By measuring the energy that is reflected by targets on earth’s surface in different wavelengths. The pattern can be identify the pattern of different fatures. It is 10^-11 to 10⁸ wavelength. Microwave 10^-2 ,Infrared 10^-5, Visible 0.5 – 10^-6,Ultraviolet 10^-8

The visible spectrum

• The light which our eyes our "remote sensors“can detect.

• Note how small the visible portion is relative to the rest of the spectrum.

• The visible wavelengths cover a range from approximately 0.4 to 0.7µm.

Violet: 0.400 - 0.446 µm

Blue: 0.446 - 0.500 µm

Green: 0.500 - 0.578 µm

Yellow: 0.578 - 0.592 µm

Orange: 0.592 - 0.620 µm

Red: 0.620 - 0.700 µm

Infra red and Thermal IR:

Infra red portion; Covers the wavelength range from approximately 0.7 µm to 100 µm.Reflected IR region (0.7 µm to 3.0 µm) is used for remote sensing purposes in ways very similar to radiation in the visible portion.

Thermal IR; region (3.0 µm to 100 µm) is quite different than the visible and reflected IR portions, as this energy is essentially the radiation that is emitted from the Earth„s surface in the form of heat. From 1µm - 6µm mid range. From 6µm - 100µm far range. The mid range is reflective and the far range is emissive radiative thermal. From 1µm - 5µm covered short wave.

Visible(reflected) IR range : It is easy to separate vegetation and water boundaries as vegetation are reflected energy and the water is absorbing the energy. Not only vegetation and water but also dry soil, wet soil, clear water and turbid water, etc.

Thermal IR range : It is possible to take images (collect data or reflect energy) with sun or without sun. We can take visible or invisible images. This process is time irrespective.