Glossary of remote sensing terms

Glossary of remote sensing terms

AIRBORNE SENSING:
Remote sensing from an airplane. (Related words: airphoto, aerial)
ANALOGUE:
This is the opposite of DIGITAL. It refers to things that aren't made up of numbers. A photo taken with a film camera would be an analogue picture. A photo taken by a digital camera would be defined in terms of zeros and ones and would be considered digital. (Related word: digital)
APPLICATION:
The end purpose for which remote sensing is used. Most often remote sensing is used to measure, map or monitor features of our environment. (See "Student's Introduction to Remote Sensing" for examples of applications) (Related word: apply)
BACKSCATTERING:
Energy, when hitting a target, can be scattered in many directions. The part of the energy that is scattered back in the exact direction where it came from, is "backscattered". (Related word: reflection)
CLOUD:
If there are clouds in the area and an optical satellite like SPOT, IRS or Landsat passes overhead, the satellite image will show the cloud but the features belowthe cloud won't be seen. A cloud shadow, the same shape as the cloud, will be seen nearby. (Related words: penetration, reflection, opaque)
CLASSIFICATION:
When image pixels are the same colour, or nearly the same colour, an image "classification" computer program can recognize this and group such pixels together. Such a grouping is called a "class" and the process of doing the grouping is called "classification". The remote sensing researcher then has the challenge of identifying just what each "class" represents in the real environment (pine trees? pavement? shallow water? dry grass?). (Related word: classes)
COMPOSITE IMAGE:
We can make a "composite" image by selecting the most appropriate parts of other images. For instance, we could take only the cloud-free parts ofmany images to make a "composite" image of all of Canada showing no clouds at all. It would not be a realistic scene, since we always have some clouds, but it would show all of Canada without allowing cloud cover to mask parts of it. (Related words: combining, mosaic)
DETECTION:
If you are detecting something, you are trying to determine if it is there. This could be done using your senses or by using instruments. Once it is found, it has been detected. (Related words: sensing, discovery, detect)
DIGITAL DATA:
Information that is made up of numbers is digital data. Telephone numbers are digital data, so are the percentage scores on your last test. So are digital images from satellites. The opposite of digital is ANALOGUE. (Related words: digitized, analogue)
DIGITAL ANALYSIS:
If you have a digital satellite image, then it's useful to analyze it digitally. Special computer programs are available for this. Such programs can stretch and distort a digital image to make it fit a map, they can enhance it to make it show some features more clearly, they can classify the image into categories which contain similar features, and much more. (Related words: image analysis, classification, enhancement)
EARTH OBSERVATION:
Looking down at the Earth from aircraft and satellites using various sensors which make images that are afterwards used to study what is happening on or near the Earth's surface. (Related word: remote sensing)
ELECTROMAGNETIC SPECTRUM:
The range of energy which contains parts or "bands" such as the visible, infrared, ultraviolet, microwave (radar), gamma ray, x-ray, radio, and which travels at the speed of light. Different parts of the electromagnetic spectrum have different wavelengths and frequencies. (Related words: spectrum, radiation, spectral band)
EMIT:
This word means the same as "sent out" or "given off". The sun emits radiation, some of which we can feel as heat and some of which we can see as light. The radar sensor in RADARSAT emits a radar beam. (Related words: transmit, radiation)
ENHANCEMENT:
Anything that you do to an image to make it simpler, faster or more accurate to analyze and interpret by eye is a form of "enhancement". Special enhancement techniques can improve colour, brightness, contrast, sharpness, etc. (Related words: visual interpretation)
GROUND STATION:
See RECEIVING STATION
GROUND TRUTHING:
Remote sensing analysts must be sure that their image analysis is accurate. This is done by field where they go out to the actual places shown in the images and confirm that what they think they see on the image is actually true. (Related words: verification, calibration)
IMAGE:
The picture that is a result of the sensing process. A remote sensing image can be displayed on a computer monitor or it can be made into a printed copy. (Related word: imagery)
IMAGE ANALYSIS:
This is the process of studying an image in order to explain, measure, map, count or monitor what is on the Earth's surface. (Related words: interpretation, classification)
LANDSAT:
Owned and launched by the United States, this is a series of remote sensing satellites that use the visible and infrared parts of the spectrum to record images of the Earth's surface. (Related words: SPOT, IRS, RADARSAT, NOAA, satellite)
LINE-OF-SIGHT:
When two objects (such as a satellite and a receiving station) have nothing in between them, then they are in "line-of-sight" of each other. When a satellite is on the other side of the Earth from a receiving station, the Earth is in between them, so the satellite and the receiving station are not in "line-of sight" of each other. (Related words: visibility, data reception)
MONITORING:
Keeping track of how things change over time. For example, with remote sensing, using several images taken over time, you can monitor the result of logging in a forest or how much of an oil slick in the ocean has been cleaned up or how well crops are growing or how much a glacier has melted or how far a plume of sediment travels in a lake, etc. (Related words: change detection, multi-temporal analysis)
MOSAIC:
A big image made by combining smaller images. For example, to get an image of a whole province in Canada, we must combine many images. This is tricky because the images were probably taken at different times and possibly in different seasons so they could look different in colour or brightness.
ORBIT:
The path traced by a satellite as it passes around a planet. (Related words: path, satellite, near polar, geostationary)
PIXEL:
The smallest unit in a digital image. A satellite image is made up of a matrix of many pixels, each having its own digital value. (Related words: image, digital analysis)
PLATFORM:
This is what carries a sensor - usually a satellite or an airplane. But a remote sensing platform could also be a hot-air balloon, a tall tower, etc. (related words: satellite, aircraft, sensor)
RADAR SHADOW:
Just as with a flashlight, a radar sensor "illuminates" a scene, and if an object blocks the beam, a shadow area develops behind it. Such shadows can be seen in a radar image. Radar shadows are pure black - they contain absolutely no information. (Related word: radar beam)
RADARSAT:
This is the first Canadian remote sensing satellite. It uses radar technology to capture images of the earth's surface. (Related words: satellite, radar)
RECEIVING STATION:
At a receiving station, antennas collect the signals sent by an orbiting satellite. Electronic devices process the signals and the data are stored. Usually the station also converts the data into usable digital and printed images. (Related words: satellite, reception, downlink)
REFLECTION:
Reflection occurs when radiation (light, radar signals, etc.) bounces off a target. It is very important in remote sensing how that reflection happens, how much is reflected and how the radiation is changed in the process of reflection, because it tells us much about the target that caused the reflection.
REMOTE SENSING:
Remote sensing is the action of collecting images or other forms of data about the surface of the Earth, from measurements made at some distance above the Earth, processing these data and analyzing them. (Related words: earth observation, environmental monitoring)
RESOLUTION:
Spatial resolution describes how clearly you can see detail in a picture. Consider the focussing done by a camera. If the picture is blurry and you can't see small objects, the resolution is poor (low resolution). If the picture is sharp and you can see small objects, the resolution is good (high resolution). Resolution is also used in describing colour detail (how similar colours are) and even time detail (how close in time things happen). (Related words: detail, image analysis)
SATELLITE:
A satellite is a natural or man.made object continuously orbiting above the Earth or another planet or star. A remote sensing satellite carries one or more instruments for recording images of the Earth, which are transmitted to a receiving station using radio waves. (Related words: platform, receiving station, orbit)
SCANNER:
While a camera would take a picture of an area all at once, a scanner is a device that examines an area point by point until the entire area has been imaged. These points become the pixels in a digital remote sensing image.
SENSOR:
A sensor is the device that records a remote sensing image, much like a camera. (Related words: scanner, platform)
SPECTRUM:
See ELECTROMAGNETIC SPECTRUM
TARGET:
Targets are the features being studied in a remote sensing image. (Related words: backscatter, reflection)
TRANSMIT:
Energy that passes through an object or material is "transmitted". This is in contrast to energy that may be reflected or absorbed. A window (which is not too dirty) allows light to transmit through and thus we are able to see through glass. (Related words: reflect, absorb, backscatter)