As was noted in the previous section, the first requirement for remote sensing is to have an energy source to illuminate the target (unless the sensed energy is being emitted by the target). This energy is in the form of electromagnetic radiation. All electromagnetic radiation has fundamental properties and behaves in predictable ways according to … Continue reading “Electromagnetic Radiation”
As was noted in the previous section, the first requirement for remote sensing is to have an energy source to illuminate the target (unless the sensed energy is being emitted by the target). This energy is in the form of electromagnetic radiation.
All electromagnetic radiation has fundamental properties and behaves in predictable ways according to the basics of wave theory.
Electromagnetic radiation consists of an electrical field (E) which varies in magnitude in
a direction perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light (c). Two characteristics of electromagnetic radiation are particularly important for understanding remote sensing. These are the wavelength and frequency.
1.1 What is Remote Sensing?
So, what exactly is remote sensing? For the purposes of this tutorial, we will use the following definition:
“Remote sensing is the science (and to some extent, art) of acquiring information about the Earth’s surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information.”
In much of remote sensing, the process involves an interaction between incident radiation and the targets of interest. This is exemplified by the use of imaging systems where the following seven elements are involved. Note, however that remote sensing also involves the sensing of emitted energy and the use of non-imaging sensors.
1. Energy Source or Illumination (A) – the first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest.
2. Radiation and the Atmosphere (B) – 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.
3. Interaction with the Target (C) – 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.
4. Recording of Energy by the Sensor (D) – 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.
5. Transmission, Reception, and Processing (E) – 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).
6. Interpretation and Analysis (F) – the processed image is interpreted, visually and/or digitally or electronically, to extract information about the target which was illuminated.
7. Application (G) – 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.
These seven elements comprise the remote sensing process from beginning to end. We will be covering all of these in sequential order throughout the five chapters of this tutorial, building upon the information learned as we go. Enjoy the journey!
Table of Contents
1.1 What is Remote Sensing? 5
1.2 Electromagnetic Radiation 7
1.3 Electromagnetic Spectrum 9
1.4 Interactions with the Atmosphere 12
1.5 Radiation – Target 16
1.6 Passive vs. Active Sensing 19
1.7 Characteristics of Images 20
1.8 Endnotes 22
Did You Know 23
Whiz Quiz and Answers 27
2.1 On the Ground, In the Air, In Space 34
2.2 Satellite Characteristics 36
2.3 Pixel Size, and Scale 39
2.4 Spectral Resolution 41
2.5 Radiometric Resolution 43
2.6 Temporal Resolution 44
2.7 Cameras and Aerial Photography 45
2.8 Multispectral Scanning 48
2.9 Thermal Imaging 50
2.10 Geometric Distortion 52
2.11 Weather Satellites 54
2.12 Land Observation Satellites 60
2.13 Marine Observation Satellites 67
2.14 Other Sensors 70
2.15 Data Reception 72
2.16 Endnotes 74
Did You Know 75
Whiz Quiz and Answers 83