Definition of Remote Sensing
Remote Sensing – The non-contact recording of information from the ultraviolet-visible, infrared, and microwave regions of the electromagnetic spectrum by means of instruments such as cameras, scanners, lasers, linear arrays, and/or spacecraft, and the analysis of acquired information by means of visual and digital image processing.
Terminologies
Photogrammetry
The art or science of obtaining reliable measurement by means of photography.
Photographic Interpretation
The act of examining photograph images for the purpose of identifying objects and judging their significance.
Remote Sensing (RS)
The measurement or acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study.
In-Situ Data Collection
It involves the scientists/engineers going out in the field and examining the object or the phenomena.
Includes:
- Questionnaires
- Observations
- Measurements
The disadvantage of in-situ data collection:
- Method-Produced Errors,
- Intrusive,
- Biased Sampling.
Remote Sensing – Art, Science, and Technology
- Science is the broad field of human knowledge concerned with facts held together by principles (Math and logic, physical sciences, biological sciences, and social sciences).
- Art is the process of visual image interpretation through the background knowledge that a person has obtained throughout their lifetime.
- Technology is a set of tools that helps in answering fundamental questions such as “how many”, “how did it happen” and “what belongs together”
Photogrammetry and Remote Sensing
-The art, science, and technology of acquiring reliable information regarding physical objects and environment, through the process of recording, measuring, and interpreting imagery and digital representation of energy patterns derived from non-contact sensor systems.
The Object
The electromagnetic radiations emitted or reflected from an object or geographic area are used as a replacement for the actual property under investigation.
The electromagnetic energy is then turned into information using visual and/or digital image processing techniques.
Sensors can obtain specific information about an object or the geographic extent of a phenomenon.
The Sensor
Remote sensing is performed using an instrument referred to as the sensors that are capable of recording different portions of the electromagnetic radiation that travels at a velocity of 3X108 m s -1 from the source, directly through the vacuum of space, or indirectly by reflection or re-radiation to the sensor.
How Far is Far?
No clear distinction about how great this distance should be Virtually all astronomy is based on remote sensing Generally:
- Less than 20 km – Sub-orbital or Air-borne
- More that 20 km – Orbital or Space-borne
RS Platforms
- Ground Based
- Airplane Based
- Satellite Based
Remote Sensing Process
Statement of the Problem
Logic Selection
Inductive – Unbiased observation, classification, generalization and theory formulation.
Deductive – Emphasis on the theory formulation and null hypothesis testing through observations.
Technological – Extraction of thematic information without using inductive or deductive logic
Hypothesis Formulation
Data Collection
Spectral Resolution is the number and dimension of specific wavelength intervals in the electromagnetic spectrum to which a remote sensing instrument is sensitive. It includes spectral bandwidth, spectral band number, and spectral range.
Classification of remote sensing data on the basis of the band numbers
- Panchromatic One band
- Multi-spectral
- Hyper-spectral
Classification of Remote Sensing data on the basis of Spectral Range
- Ultraviolet (UV)
- Visible and Near Infrared (VNIR)
- Short Wave Infrared (SWIR)
- Thermal Infrared (TIR)
- Radio Detection and
- Ranging (RADAR)
Types of Remote Sensing Data Resolution
1- Spectral Resolution
2- Spatial Resolution
3- Temporal Resolution
4- Radiometric Resolution
Spectral resolution
Describes the ability of a sensor to define fine wavelength intervals.
The finer the spectral resolution, the narrower the wavelength range for a particular channel or band.
Spatial Resolution
A measure of the accuracy or detail of a graphic display expressed as dots per inch, pixels per line, lines per millimeter, etc. It is a measure of how fine an image is, usually expressed in dots per inch (dpi).
Instantaneous-Field of View (IFOV) of the sensor defines the nominal spatial resolution of the remote sensing system.
Temporal Resolution
Temporal resolution is the revisit period, and is the length of time for a satellite to complete one entire orbit cycle, i.e. start and back to the exact same area at the same viewing angle.
For example, Landsat needs 16 days, MODIS needs one day, NEXRAD needs 6 minutes.
Radiometric Resolution
Radiometric Resolution is the sensitivity of a remote sensing sensor to the difference in signal strength as it records the radiant flux reflected or emitted from the terrain. In digital remote sensing data, Radiometric Resolution is referred to as Bit Data and is reported in terms of Digital Numbers (DN) values reflecting different shades of gray.
The DN value of Zero is pure Black and the DN value of 255 is pure white. The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in energy.
| Bit | Shades of Grey |
| 1 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 16 |
| 5 | 32 |
| 6 | 64 |
| 7 | 128 |
| 8 | 256 |
Radiometric Resolution of the Human Eye
The Human Eye has a radiometric resolution that ranges between 3 and 4 bit. That is to say, the human eye can not differentiate between more than 16 shades of gray.
On the other hand, the human eye is capable of distinguishing about 7 million colors.
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