GLS280/GEO280: INTRODUCTION TO REMOTE SENSING Basic Principles of Remote Sensing
INTRODUCTION
Definition
Remote sensing is the science and arts of obtaining information about an object, area and phenomenon through the analysis of data collected by a device that is not in contact with the object, area or phenomenon under investigation. (Lillesand & Kiefer, 2000).
Simple example: your eyes – you are employing remote sensing when you reading this notes!
Your eyes capture some amount of light which reflected from this page. Then it was analyzed, or interpreted in your ‘mental computer’ to enable you to explain or understanding the words.
Using various sensors, we remotely collect data that may be analyzed to obtain information about an object, areas or phenomena being investigated. The remotely collected data can be of many forms, including variations in force distributions, acoustic wave distributions or electromagnetic energy distributions.
Eg:
Gravity meter acquires data from distributions of force of gravity
Bat’s navigations – obtain data in acoustic wave distributions
Our eyes – acquires data in electromagnetic energy distributions
Other Definitions:
- Remote sensing is the acquiring of data without touching it.
(Colwell, 1984)
- Remote sensing is a non contact recording of information from the ultraviolet, visible, infrared, and microwave regions of the electromagnetic spectrum by means of instruments such as cameras, lasers, scanners, linear arrays, and/or area arrays
Differences between direct and remote sensing
Differences Remote Sensing Direct Measurement Time - depend on application and
objective
- usually faster and effective
- time consuming
- depend to the area and objective of the application
Area covered - can cover large and small area effectively
- practical for small area application
Access to the area
- no need to be on site for data collection
- remotely collect data from sensors
- should be on site with the measurement devices
- some study area is difficult to access
Disturbance levels
- depend on sensors,
atmosphere, weathers condition.
- depend on location, securities issues, government policies, and etc
Cost
effectiveness
- depend on technology
- usually practical for large area
- cheaper than Remote sensing
- but time consuming and costing for large area.
Remote sensing:
A technology used for obtaining information about a target/object through the analysis of data acquired from the target/object at a distance.
It is composed of 3 parts:
the targets - objects or phenomena in an area;
the data acquisition - through certain instruments; and
the data analysis - again by some devices
Figure 1: Data Acquisition and Data Analysis
THE REMOTE SENSING PROCESS
Basic remote sensing process involved was data acquisition and data analysis. Data acquisition was done through certain process or elements. Data analysis process involved examining the data using various viewing and interpretation devices to analyzed data or pictorial data or using computer to analyze digital sensor data.
Element of Remote Sensing Process
a) Electromagnetic Radiation b) Atmosphere
c) Earth attributes/resources d) Platforms/sensors
e) Data products
Figure 2: Remote Sensing Process
a) Electromagnetic Radiation
Electromagnetic radiation (EMR) was illuminated by the sun or solar. The first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest
b) Atmosphere
As the energy travels from its source to the target, it will come in contact with and interact with the atmosphere it passes through. This interaction may take place a second time as the energy travels from the target to the sensor.
c) Earth attributes/resources
once the 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.
d) Platforms/sensors
after the energy has been scattered by, or emitted from the target, we require a sensor (remote - not in contact with the target) to collect and record the electromagnetic radiation.
A
B
D
C
E
F
e) Data products
The energy recorded by the sensor has to be transmitted, often in electronic form, to a receiving and processing station where the data are processed into an image (hardcopy and/or digital).
f) Interpretation and analysis
The processed image is interpreted, visually and/or digitally or electronically, to extract information about the target which was illuminated. The final element of the remote sensing process is achieved when we apply the information we have been able to extract from the imagery about the target in order to better understand it, reveal some new information, or assist in solving a particular problem.
DATA ACQUISITION AND REMOTE SENSING DATA REQUIREMENT
In Remote Sensing (R.S) system, the data was obtained remotely through certain devices or tools such as platforms and sensors and how electromagnetic energy or signals that contained the data are detected, recorded and interpreted.
Data acquisition system for RS includes two parts:-
Platforms
Types of platforms used in data acquisition
• Aircraft
• Satellites
• Balloons
• Rockets
• space shuttles, etc
The instruments / Sensors
Remote sensing is performed using instruments, often referred to as a sensor. The majority of remote sensing instruments record EMR that travels at a velocity of 3 x 108 ms-1 from the
non-photographic instruments, such as:
- Radiometers
- Electro-optical scanners - Radar systems, etc
Information about an area and target
Sensors can obtained much specified areas and target such as a diameter of a trees or geographic extent of phenomenon such as polygonal boundary of the forest. The electromagnetic energy emitted or reflected from an object or geographic areas is used as a surrogate for actual property under investigation. The electromagnetic energy measurements must be turned into information using visual or digital image processing methods.
Remote Sensing Data
Data collection in remote sensing may take place directly in the field (in situ/place) or at some remote distance from the object or area of interest. Remotely sensed data is a data about geographic area acquired using specialized instruments and sensors without direct contact with the specific area on the earth or without going to that area of interest.
Reference data / In Situ Data Requirements
The acquisition of reference data was including collecting collateral data and in situ data about the phenomena that are being sensed remotely. The data may be needed for a particular analysis. For examples, the data needed might be derived from a soil map, water quality laboratory report, and condition of agricultural crops, land uses, tree species, survey data, and ground truth.
In situ data always referred as a field data. This data collection process involves the person or researcher to go to the field and find out the phenomena of interest. For examples, they take GPS points to verify the ground control points for geometric correction process. The researcher may use a transducer or other in situ measurement devices to collect the data.
Referenced data might be used to serve any or all the following purposes:-
To aid in the analysis and interpretation of remotely sensed data.
To calibrate a sensor.
To verify the information extracted from remote sensing data.
SUCCESSFUL REMOTE SENSING APPLICATION
The role of people in remote sensing process:-
“A thorough understanding of a problem at hand is paramount to the productive application of any remote sensing methodology”. (Lillesand & Kiefer, 2000).
The minimum components that all design of successful remote sensing efforts should involve are:
Clearly defined problems.
Evaluation of remotely sensed data as a suitable solution.
Identify required remotely sensed data.
Selection of appropriate processing methodology and reference data.
Establish criteria for error or accuracy assessment.
Application of Remote Sensing
Vegetations/Crops
Terrestrial (land use/land cover)
Oceanic (Surface/seafloor)
Disasters management
Geology and geomorphology
Environmental problems, etc
HISTORY OF REMOTE SENSING TECHNOLOGY
The following is a brief list of the times when innovative development of remote sensing were documented:
