مبادئ الاستشعار عن بعد

Introduction to Remote Sensing

Introduction to Remote Sensing
المشكلة: دراسة الأحوال الجوية، حماية البيئة، تلوث الهواء، الكوارث الطبيعية، ...لحل أي مشكلة نحتاج إلى جمع معلومات، وجمع المعلومات يحتاج إلى جهد وزمن وتكاليف باهظة.

What is remote sensing ?

Remote – away from or at a distanceSensing – detecting a property or characteristic

Remote Sensing

The term "remote sensing," first used in the United States in the 1950s by Ms. Evelyn Pruitt of the U.S. Office of Naval Research

Definitions

"Remote sensing is teaching us a new way of seeing". Remote sensing has been defined in many ways.

Definition (1)

Definition (2)


Definition (3)

Definition (4)

Definition (5)

الإستشعار عن بعد علم يختص بجمع المعلومات عن هدف ما من مسافة بعيدة دون أن يكون هناك اتصال مباشر بين الهدف وجهاز الالتقاط وذلك باستخدام خواص الموجات الكهرومغناطيسية المنبعثة أو المرتدة أو المنعكسة.

Brief History of Remote Sensing

1839, the first photographs. 1849, used photography in topographic mapping. 1858, balloons were being used to acquire photography of large areas.

1925-1945

Mid 1930s, color photography. Aerial photography became widespread during World War II, with improved lenses and platform stability, enemy positions and military installations could be identified from aircraft. Radar

1945-1960

1960-1972
This was the age of instrument development. In 1964, the Nimbus satellite series of experimental meteorological remote sensing was initiated. By 1966, meteorological satellites moved from being experimental to being operational with the introduction of the ESSA series of satellites which included Automatic Picture. The Defense Meteorological Satellite Program (DMSP) was started by the U.S. Air Force in 1966. 1972, Landsat 1 (also referred to as Earth Resources Technology Satellite.



1972-present
1975: The Synchronous Meteorological Satellites. 1976: Laser Geodynamic Satellite I. 1978: The Heat Capacity Mapping Mission. 1978: Seasat demonstrated techniques for global monitoring of the Earth's oceans. 1978: Nimbus 7, the final satellite in that series, was launched. 1984: The Earth Radiation Budget (ERBE) satellite began its study of how the Earth absorbs and reflects the Sun's energy. 1991: The Upper Atmosphere Research Satellite (UARS) began its study of the chemistry and physics of the Earth's atmosphere. Today, the GOES (Geostationary Operational Environmental Satellite) system of satellites provides most of the remotely sensed weather information for North America.

The element of the remote sensing process

Energy Source or Illumination Radiation and the Atmosphere Interaction with the Target Recording of Energy by the Sensor Transmission, Reception, and Processing Interpretation and Analysis Application

Recording of Energy by the Sensor

Active and Passive Remote Sensing systems
Passive: The sensor records energy that is reflected or emitted from the source, such as light from the sun. This is also the most common type of system.

Passive remote sensors

Radiometer Imaging Radiometer Spectrometer Spectroradiometer

Active and Passive Remote Sensing systems

Active: where the object is illuminated by radiation produced by the sensors, such as radar or microwaves.



Active remote sensors
Radar (Radio Detection and Ranging) Scatterometer Lidar (Light Detection and Ranging)

Uses of Remote Sensing

Weather: It is possible now to get immediate information on climate and weather conditions from remote sensing satellites. Images over time allow us to predict weather behavior.

Uses of Remote Sensing

Agriculture: Crop mapping and yield prediction; crop damage due to storm, drought or disease and insect outbreaks.

Uses of Remote Sensing

Environmental Impacts: Remote Sensing to determine oil spill size, location, direction and magnitude of movement.
Coastal oil spill, Wales, England

Uses of Remote Sensing

Forestry Inventory: Remote Sensing used for forest inventory, mapping cut-overs, forest fire mapping, species identification.

Uses of Remote Sensing

Geological Mapping: Mapping faults, folds, lineaments, rock types and petroleum engineering.

Principles of Object Identification(1)

Shape: this characteristic alone may serve to identify many objects. Examples include the long linear lines of highways, the intersecting runways of an airfield, the perfectly rectangular shape of buildings, or the recognizable shape of an outdoor baseball diamond.

Principles of Object Identification(2)

Size: noting the relative and absolute sizes of objects is important in their identification. The scale of the image determines the absolute size of an object. As a result, it is very important to recognize the scale of the image to be analyzed.

Principles of Object Identification(3)

Image Tone or Color: all objects reflect or emit specific signatures of electromagnetic radiation. In most cases, related types of objects emit or reflect similar wavelengths of radiation. Also, the types of recording device and recording media produce images that are reflective of their sensitivity to particular range of radiation.

Principles of Object Identification(4)

Pattern: many objects arrange themselves in typical patterns. This is especially true of human-made phenomena.

Principles of Object Identification(5)

Shadow: shadows can sometimes be used to get a different view of an object. For example, an overhead photograph of a towering smokestack or a radio transmission tower normally presents an identification problem. This difficulty can be over come by photographing these objects at sun angles that cast shadows. These shadows then display the shape of the object on the ground. Shadows can also be a problem

Principles of Object Identification(6)

Texture: imaged objects display some degree of coarseness or smoothness. This characteristic can sometimes be useful in object interpretation. For example, we would normally expect to see textural differences when comparing an area of grass with a field corn. Texture, just like object size, is directly related to the scale of the image.

Maps & Cartography

Maps have three main attributes: Scale Projection Symbolization

Map projections

Cylindrical Projection

Conic Projection

Planar Projection

Map Symbolization

How is Energy Transferred?



Electromagnetic radiation

The wavelength is the length of one wave cycle,

Frequency
Frequency refers to the number of cycles of a wave passing a fixed point per unit of time. Frequency is normally measured in hertz (Hz),

Wavelength and frequency are related by the following formula:

Frequency,  is inversely proportional to wavelength, The longer the wavelength, the lower the frequency, and vice-versa.

Scattering

Once electromagnetic radiation is generated, it is propagated through the earth's atmosphere almost at the speed of light in a vacuum. Unlike a vacuum in which nothing happens, however, the atmosphere may affect not only the speed of radiation but also its wavelength, intensity, spectral distribution, and/or direction.

Scattering

Scatter differs from reflection in that the direction associated with scattering is unpredictable, whereas the direction of reflection is predictable. There are essentially three types of scattering: • Rayleigh, • Mie, and • Non-selective.


Atmospheric Scattering
Type of scattering is a function of: the wavelength of the incident radiant energy, and the size of the gas molecule, dust particle, and/or water vapor droplet encountered.

Rayleigh scattering

Rayleigh scattering occurs when the diameter of the matter (usually air molecules) are many times smaller than the wavelength of the incident electromagnetic radiation. The amount of scattering is inversely related to the fourth power of the radiation's wavelength. For example, blue light (0.4 m) is scattered 16 times more than near-infrared light (0.8 m).

Rayleigh scattering

Rayleigh scattering is responsible for the blue sky. Rayleigh scattering is responsible for red sunsets.

Mie scattering

Mie scattering takes place when there are essentially spherical particles present in the atmosphere with diameters approximately equal to the wavelength of radiation being considered. The amount of scatter is greater than Rayleigh scatter and the wavelengths scattered are longer.

Non-selective scattering

Non-selective scattering is produced when there are particles in the atmosphere several times the diameter of the radiation being transmitted. Scattering can severely reduce the information content of remotely sensed data to the point that the imagery looses contrast and it is difficult to differentiate one object from another.

Absorption

Absorption is the process by which radiant energy is absorbed and converted into other forms of energy.the atmosphere does not absorb all of the incident energy but transmits it effectively. Parts of the spectrum that transmit energy effectively are called “atmospheric windows”.

Absorption of the Sun’s Incident Electromagnetic Energy in the Region from 0.1 to 30 m by Various Atmospheric Gases window

Reflectance

Reflectance is the process whereby radiation “bounces off” an object like a cloud or the terrain.The angle of incidence and the angle of reflection are equal.

Index of Refraction

The index of refraction (n) is a measure of the optical density of a substance. This index is the ratio of the speed of light in a vacuum, c, to the speed of light in a substance such as the atmosphere or water, cn (Mulligan, 1980):The speed of light in a substance can never reach the speed of light in a vacuum. Therefore, its index of refraction must always be greater than 1. For example, the index of refraction for the atmosphere is 1.0002926 and 1.33 for water. Light travels more slowly through water because of water’s higher density.

Snell’s Law Refraction can be described by Snell’s law, which states that for a given frequency of light (we must use frequency since, unlike wavelength, it does not change when the speed of light changes), the product of the index of refraction and the sine of the angle between the ray and a line normal to the interface is constant:From the accompanying figure, we can see that a nonturbulent atmosphere can be thought of as a series of layers of gases, each with a slightly different density. Anytime energy is propagated through the atmosphere for any appreciable distance at any angle other than vertical, refraction occurs.

Atmospheric Refraction

Refraction in three nonturbulent atmospheric layers. The incident energy is bent from its normal trajectory as it travels from one atmospheric layer to another. Snell’s law can be used to predict how much bending will take place, based on a knowledge of the angle of incidence (q) and the index of refraction of each atmospheric level, n1, n2, n3.

The element of the remote sensing process

Energy Source or Illumination Radiation and the Atmosphere Interaction with the Target Recording of Energy by the Sensor Transmission, Reception, and Processing Interpretation and Analysis Application

Recording of Energy by the Sensor

Blackbody Radiation Curves



Path 4 contains radiation that was reflected or scattered by nearby terrain ( ) covered by snow, concrete, soil, water, and/or vegetation into the IFOV of the sensor system. The energy does not actually illuminate the study area of interest. Therefore, if possible, we would like to minimize its effects. Path 2 and Path 4 combine to produce what is commonly referred to as Path Radiance, Lp.
Jensen 2007


Path 5 is energy that was also reflected from nearby terrain into the atmosphere, but then scattered or reflected onto the study area.
Jensen 2007

The total radiance reaching the sensor from the target

The total radiance recorded by the sensor becomes: