Introduction: Theoretical and Technical Perspectives of Remote

Sensing; Special Applications

The main theme is tied to the use of satellites as orbiting platforms that mount

sensors devoted to compiling the data resulting from some mode(s) of remote

sensing.

The Concept of Remote Sensing

• "what does it mean?

• familiar activity that we all do as a matter of daily life, but that gets complicated when we increase the scale at which we observe. As you view the screen of your computer monitor, you are actively engaged in remote sensing.

Remote sensing meaning

• refers to instrument-based techniques employed in the acquisitionand measurement of spatially organized (most commonly, geographically distributed) data/information on some property(ies) (spectral; spatial; physical) of an array of target points (pixels) within the sensed scene that correspond to features, objects, and materials, doing this by applying one or more recording devices not in physical, intimate contact with the item(s) under surveillance (thus at a finite distance from the observed target, in which the spatial arrangement is preserved); techniques involve amassing knowledge pertinent to the sensed scene (target) by utilizing electromagnetic radiation, force fields, or acoustic energy sensed by recording cameras, radiometers and scanners, lasers, radio frequency receivers, radar systems, sonar, thermal devices, sound detectors, seismographs, magnetometers, gravimeters, scintillometers, and other instruments.

the principal ideas within this definition, make a list of key words in it.ANSWER Acquisition/measurement; data/information; properties;

phenomenon,...material; recording device; not in contact; measuring fields.radiation;

instruments.)

What is the meaning of "geospatial"? Are there any differences in meaning of the terms

"features", "objects", and "classes"? • Geospatial connotes the distribution of something in a geographic

sense; it refers to entities that can be located by some co-ordinate system. The three terms "feature; object; class" have different but somewhat overlapping meanings. Feature can refer to "overall appearance", "mark", or "characteristic", and/or to a set of measurable properties, or, more narrowly, to a specific geometric or geomorphic entity on the surface of a planet such as Earth. Objectrelates to a single entity, of a physical nature, capable of being sensed (e.g., seen or touched), to which a descriptive name can be given, such as "house", "road". Class has a more general connotation, pointing to a group of features or objects of identical or similar types that have taxonomic significance; examples are "forest"; "urban"; "mountains". Classes can be hierarchical, that is, can be subdivided into subclasses; thus "urban" includes "inner city/suburbia", "road networks", "neighborhoods", "shopping centers", etc.

The idea of remote sensing carries with it a number of objectives and ancillary operations, each with its own "buzz word". Here is a diagram that connotes this

concept, as it applies to the services offered by a specific remote sensing commercial company (IIRMR):

Principles of Remote SensingThe Photon and Radiometric Quantities

• A photon travels as an EM wave having two components, oscillating as sine waves mutually at right angles, one consisting of the varying electric field, the other the varying magnetic field

Measuring the varying energy levels of a single entity, the fundamental unit in the electromagnetic (which may be abbreviated "EM") force field known as the photon.

Sensor Technology - Types of Resolution

• Most remote sensing instruments (sensors) are designed to measure photons.

SCANNER

The Pixel• Each line is subdivided into a sequence of individual

spatial elements that represent a corresponding square, rectangular, or circular area (ground resolution cell) on the scene surface being imaged (or in, if the target to be sensed is the 3-dimensional atmosphere).

• Thus, along any line is an array of contiguous cells from each of which emanates radiation. The cells are sensed one after another along the line. In the sensor, each cell is associated with a pixel that is tied to a microelectronic detector. Pixel is a short abbreviation for Picture Element, a pixel being a single point in a graphic image.

• Each pixel is characterized by some single value of radiation (e.g., reflectance) impinging on a detector that is converted by the photoelectric effect into electrons. For moving systems, such as sensors on an orbiting satellite, there is a time element for signal duration within each pixel in that the detector that activates it records the radiation for a brief moment,

• On color monitors, each pixel is actually composed of three dots -- a red, a blue, and a green one. Ideally, the three dots should all converge at the same point, but all monitors have some convergence error that can make color pixels appear fuzzy.

• The quality of a display system largely depends on its resolution, how many pixels it can display, and how many bits are used to represent each pixel.

• VGA systems display 640 by 480, or about 300,000 pixels. In contrast, SVGA systems display 800 by 600, or 480,000 pixels.

• True Color systems use 24 bits per pixel, allowing them to display more than 16 million different colors. The idea of a pixel can be grasped visually with this illustration (shown again and discussed in terms of a mixed pixel in Section 13):

• The common sense definition of spatial resolution is often simply stated as the smallest size of an object that can be picked out from its surrounding objects or features. This separation from neighbors or background may or may not be sufficient to identify the object. Compare these ideas to the definition of three terms which have been extracted from the Glossary of Appendix D of this Tutorial:

• resolution-Ability to separate closely spaced objects on an image or photograph. Resolution is commonly expressed as the most closely spaced line-pairs per unit distance that can be distinguished. Also called spatial resolution.

• resolution target-Series of regularly spaced alternating light and dark bars used to evaluate the resolution of images or photographs.

• resolving power-A measure of the ability of individual components. and of remote sensing systems, to separate closely spaced targets.