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Glossary
A B
C D E F
G H I J
K L M N
O P Q R
S T U V
W X Y Z
A
Absorption
Reduction in the amount of light or radiation being transferred
though a medium
Absorption Coefficient
Measurement of the amount of sunlight absorbed per metre depth
of water
Active Sensors
Sensors with their own source of radiation, e.g. laser altimeters,
imaging radar and acoustic systems
Accuracy
Is the degree of conformity of a measured or calculated quantity
to its actual (true) value.
Air-Water Interface
Ocean-atmosphere (gas-liquid) boundary which alters the direction
and magnitude of sunlight
Airborne Laser
ctive imaging system based on a green to red laser used to
produce maps of land-surface height and bathymetry in shallow
(< 20m) and clear waters.
Airborne Radar
Active imaging system using microwave energy to measure surface
roughness and moisture content
Ali
Advanced Land Imager - next generation Landsat TM/ETM sensor
on the EO-1 platform
Algal Blooms
A rapid and extensive growth of algae on the surface, water
column or substrate
Analytical Modeling
mage processing approach used to estimate biophysical properties
(e.g. total suspended sediment concentration) by applying
radiative transfer equations to image data.
AOP's
Apparent optical properties of water - those dependent on
the strength and direction of incident sunlight, e.g. reflectance.
Atmospheric Correction
mage processing approach used to remove scattering and absorption
effects from image data so the signal used is that emanating
fro the air-water interface or land surface, not the top of
the atmosphere.
Attenuation
Distortion of true reflectance or radiance levels due to absorption
and scattering effects.
B
Backscattering Coefficient
A measure of the proportion of light at specific wavelengths
that will be backscattered - dependent on particle size and
form in water.
Bathymetry
Depth of the water column to substrate, measured relative
to a specified height datum.
Benthos
Living organisms, organic and inorganic, commonly found on
the seafloor
Beam Attenuation Coefficient
Measurement of the amount of absorption experienced by a collimated
beam of light per metre depth of water.
Biomass
The amount of "living" material associated with
a plant or organism. For plants biomass can be live and dead,
and above or below ground.
Bio-Optical Modeling
Application of radiative transfer models to understand light
interactions in aquatic media and use these to estimate water
column constituents from image data.
Biophysical Properties
Biological and physical properties of an environment
Boat Based Visual Assessments
Assessments done from a boat where a video or still cameras
is dropped in the water to visual assess an feature (e.g.
benthos) real time via a monitor in the boat or via images
later in the office.
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C
Chlorophyll A
Primary pigment used to capture sunlight for use in a plant's
photosystem during photosynthesis.
CASI
Compact Airborne Spectrographic Imager - an airborne hyperspectral
imaging system.
Calibration
A process used to initialize a mathematical model to certain
measured conditions.
CDOM
Coloured dissolved organic material
Coastal Environments
Mangrove wetlands, inter-tidal and sub-tidal sections of a
coastal embayment
Coastal Indicators
Selected biophysical parameters which have been recognised
as being sensitive to the health or condition of coastal environments.
Coastal-Marine Ecosystem Health Indicator
See Coastal indicators
Continuous Map
A map showing spatial variation in a quantitative property,
e.g. water depth, without grouping it into discrete thematic
classes.
Coordinate System
A reference system used to define location in relation to
a set origin point, i.e. [x, y, z]
Coral Habitat
An area with suitable conditions to allow the groath and maintenance
of coral reefs.
Cover Type
A type of living or non-living feature, commonly occurring
over substrate.
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D
Datum
An origin point or surface for vertical or horizontal coordinates
Diffuse Skylight
Sun-light that has been scattered by aerosol, dusts and clouds,
and is not in a direct beam.
Deep Benthic Cover
Living and non-living features covering the substrate at depths
greater than 15-20m
Diving Visual
Assessments where SCUBA diving gear is needed to visually
assess the benthos or any other feature which is out of free
diving range
Down Welling
Light moving downwards and away from the sun to the earth's
surface
Down Welling Irradiance
Sunlight incident upon a surface from all viewing angles
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E
Eo-1
NASA satellite - experimental platform for Hyperion and ALI
Environmental Variable
Bathymetry, benthic cover, water quality parameters are examples
of variables which are describing the environment.
Environmental Restrictions
Environmental conditions in the atmosphere, se asurface and
water column that affect the type and quality of remotely
sensed information able to be collected, e.g. clouds, smoke,
haze, wind, tidal currents, breaking waves, etc.
Electro Magnetic Radiation (EMR)
Energy emitted form any object with a temperature greater
than absolute zero. This includes visible and non visible
energy such as sunlight, infrared, thermal infrared and microwaves.
EMR consists of units of energy (photons) which produce electric
and magnetic field as they move through space. Different levels
of EMR energy produce different types of light.
Error Matrix
A table for comparing the mapped value or category in an image
to a reference value obtained from field survey.
F
Feasible
Feasible applications are those that have been shown to work
with experimental image data sets or over limited areas with
very small pixels or global scales with large pixels.
G
Geometric Correction Or Georeferencing
The process of converting an image into a forma where each
pixel has a projection, datum and coordinate, enabling it
to be integrated with other spatial data.
Georeferencing
See geometric correction
Graphic Sequence
One path for users to take through the toolkit where you can
either select an environmental variable to map or explore
the options for mapping from a specific sensor.
Ground Resolution Element
The smallest spatial sampling unit used by an imaging sensor
to measure reflected or emitted EMR. The GRE is displayed
as a pixel in an image.
Ground Control Points
Environmental features able to be seen on an image and on
the ground/reef, where coordinates are obtained from field
survey and are used to tie the image to ground coordinates.
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H
Habitat
The characteristic biotic and abiotic elements of an area,
in which a specific organism lives, or as the characteristic
of an area.
Hydroscat-6
Instrument designed for measuring the backscattering coefficient
of water bodies at a number different wavelengths.
Hymap
An airborne hyperspectral sensor with 126 bands from 400-2500nm
collecting images from 3m - 10m pixels. www.hyvista.com
Hyperion
Experimental satellite-borne hyperspectral imaging systems
with 30m pixels and 196 bands on the EO-1 platform.
Hyperspectral
A device is hyperspectral if it records reflected or emitted
light using > 10, narrow spectral bandwidths (cf. multispectral)
I
Ikonos
Commercially operated high spatial resolution (4m) multispectral
and panchromatic (1m) satellite imaging sensor.
Intertidal
The region between spring high-water and low-water tidal limits
which is exposed at low tide and inundated at high tide.
Intertidal Benthic Cover
Living and non-living features covering the inter-tidal substrate.
Image Corrections
Image processing operations designed to remove geometric and
atmospheric distortions in an image data set.
Image Pixel
Smallest spatial sampling unit used by an imaging sensor to
measure reflected or emitted energy from the surface of the
earth.
Inherent Optical Domain
An area of water exhibiting similar absorption and scattering
properties, hence similar water colours.
Inherent Optical Properties
Properties of the water column that do not change with illumination
strength and direction, i.e. absorption and scattering coefficients.
Irradiance Reflectance
A ratio of reflected sunlight measured over all directions
to incident sunlight measured over all directions.
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K
Kd
Vertical diffuse attenuation coefficient - an estimate of
the amount of light attenuated by water per unit depth.
L
Landsat Thematic Mapper/Enhanced Thematic Mapper
General purpose multispectral, moderate spatial resolution
imaging satellite sensors that have operate since the mid
1980s (TM) and April 1999 (ETM).
Level of Measurement Precision Required
The smallest detectable level of change in the environmental
being mapped. For example, do you need to map depth in 1cm
or 1m increments? 1cm is a higher measurement precision.
Level of Measurement Accuracy Required
The smallest difference between estimated/mapped environmental
variables and a reference value for that variable.For example,
a comparison of a seagrass species map to field survey for
a site may show an agreement or accuracy of 85% between image
and field survey data.
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M
Matrix Inversion Method
A mathematical solution to the radiative transfer equation
developed to enable its inversion to estimate concentrations
of the water column constituents responsible for the water
colour.
Mapping Needs
The information a manager, scientist, technician, student
wants to produce from an image in a spatial form. The needs
are the constraints to the project in terms of the area to
cover, smallest feature to map, what is to be mapped and when
to map it.
MERIS
Medium spectral resolution imaging spectrometer - See
http://envisat.esa.int/object/index.cfm?fobjectid=1665
Minimum Mapping Unit
The smallest spatial unit to be shown on a map
MODIS
Moderate Resolution Imaging Spectrometer - See http://modis.gsfc.nasa.gov/
Multi-Date Normalization
An image correction approach used to remove the distorting
effects of different types of atmospheric conditions over
an image of the same area collected on different dates.
Multi-Spectral
An image data collection system where reflected or emitted
energy is measured in less than 10 broad spectral bands.
Multi-Temporal
Data that has been collected for the same area over a
series of successive dates.
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N
Near Infra Red (Nir)
The non-visible 700 -1000nm portion of the EMR spectrum
Normalised Difference Vegetation Index
A normalised ratio transformation using the red and NIR pixel
values which is sensitive to vegetation cover.
O
Remote Sensing Reflectance Or R(0-)
Atmospheric and air-water interface correction of image data
produces this value in each pixel. This represents the ratio
of upwelling radiance to downwelling irradiance just below
the water surface.
Objected Orientated Classification
An approach to converting an image data to a map which works
where the pixel size is significantly smaller than the target
to be mapped. This approach identifies uniform spatial regions
in an image which are then labeled by an analyst.
Operational But Costly
Operational applications are those that have been clearly
demonstrated to work accurately from commercially available
image data and standard image processing systems, and are
delivering data at the required resolution.
Optically Deep
A water body where the bottom/substrate/benthos is not visible
due to attenuation of incident sunlight. E.g. deep and clear
water bodies or shallow and highly turbid water bodies.
Optically Shallow
A water body where the bottom/substrate/benthos is visible.
Overall Accuracy
A measure of agreement between an image based value and the
value for the same location measured on the ground or from
another data source. If both data sets agree the accuracy
the accuracy is 100%
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P
Panchromatic
All visible wavelengths of light, i.e. a panchromatic image
or photo is a black and white image of all visible bands.
Passive Sensors
Imaging sensors that measure reflected sunlight or emitted
thermal energy.
Per-pixel classification
An approach to converting an image data to a map which works
where the pixel is assumed to be made of one cover type. This
approach assigns a cover type or class label to each pixel,
so they are mapped individually.
Platform Type
The vehicle on which a sensor is mounted, e.g. satellite,
aircraft, boat, balloon, person.
Pixel Size
The linear dimensions of a square in an image which contains
the reflectance or emittance measured by a GRE
PIFS
Pseudo-Invariant Features - landscape features that retain
the same reflectance over time and can be used for image calibration.
Planimetric Projection
A map projection where each map element is at its true location
on the ground (cf. aerial photography and some satellite images
which have a perspective projection).
Precision
The level of detail with which a measurement is made, e..g
measuring depth in 1.0cm increments is more precise than measuring
at 1.0m increments.
Producer Accuracy
A term used to define the level of agreement between an image
based map of surface cover types and reference data for the
same surface cover types. If 100 reference points are collected
by the image processing technician (producer) and 80 of those
are classified correctly, the producer's accuracy is 80%.
Projection
A set of equations for transforming a 3-dimensional surface
to a planar 2-dimensional surface, i.e. for transforming 3-d
earth measurements to a 2-d map.
Positional Accuracy
The difference between a measured coordinate and its true
location or a reference value for that location.
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Q
Quickbird
Commercially operated high spatial resolution (2.68m)
multispectral and panchromatic (0.7m) satellite imaging sensor.
R
Radiative Transfer Modeling Approach
Application of equations that define the physics of how light
moves through a medium and interacts with it. It is used to
estimate the biophysical properties controlling reflection,
absorption and transmission of light.
Radiance
A standard physical unit for measuring the amount of EMR incident
on a unit area, over a unit time from a specific angle. Radiance
units are watts/m2.sr, where watts = joules/seconds and sr
= units of a solid 3-d angle, steradians.
Radiometric Correction
Conversion of image pixel digital numbers from a relative
scale to an absolute physical units scale, e.g. radiance.
Radiometric Resolution
Smallest difference in reflected light able to be detected
by a sensor and its dynamic range.
Radio-Sonde Data
Vertical profile through the atmosphere of temperature and
humidity, used for atmospheric correction.
Reflectance Signature
Ratio of upwelling radiance to downwelling irradiance on a
target, i.e. its characteristic absorption/reflectance response.
Refraction
Refraction is the change in direction of a wave due to a change
in its speed. This is most commonly seen when a wave passes
from one medium to another. Refraction of light is the most
commonly seen example, but any type of wave can refract when
it interacts with a medium, for example when sound waves pass
from one medium into another.
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S
Satellite Radar
A side-looking imaging system that is active and is able to
operate independent of sunlight.
Scattering
The process by which photons of light change the direction
they are traveling due to a collision/interaction with a particle
or molecule. Blue sky is produced by scattering of photons
of blue light.
Shallow Benthic Cover
Living and non-living features covering the substrate at depths
shallower than 15-20m
Secchi Depth
Commonly used approach to measure the clarity of a water body
by dropping a black/white disk and noting the depth at which
the black and white is no longer visible.
Sensor Type
Differences between imaging sensors are due to the type of
sensor (passive or active), spatial resolution, spectral bands
used and radiometric resolution.
Side Scan Sonar
A boat or UAV mounted active imaging system for mapping the
seabed for a wide variety of purposes.In conjunction with
seafloor samples it is able to provide an understanding of
the differences in material and texture type of the seabed.
Snorkelling Visual Survey
Assessments where a snorkeler can visually assess the benthos
or any other feature underwater which requires no SCUBA diving
gear.
Spatial Resolution
A measure of the scale of the smallest feature able to be
detected on an image.
Spatial Dimensions
The spatial attributes of an image or imaging sensor, referring
to (1) the pixel size; and (2) the extent of the area covered
by the image.
Spectral Dimensions
The type of reflected or emitted light recorded by a sensor,
referring to (1) the position of spectral bands, e.g. blue,
green, red; (2) width of spectral bands; and (3) number of
spectral bands.
Spectral Signature
See reflectance signature
Spectral Angle Mapping
An image classification approach used to group pixels with
similar reflectance signature.
Spot Xs
Commercially operated high-moderate spatial resolution (20m)
multispectral and panchromatic (5m) satellite imaging sensor
Striping Effects
Artifacts introduced in coastal Landsat sensor scenes due
to scanner variations every 16 lines.
Submerged Aquatic Vegetation (SAV)
Aquatic vegetation, such as sea grasses, that cannot withstand
excessive drying and therefore live with their leaves at or
below the water surface.
Substrate Features
See substrate types
Substrate Types
Types of material found on seafloor: sand, rock, seagrass,
algae etc…
Subsurface Irradiance
Reflectance Similar quantity as R(0-), except this is measured
as a ratio of upwelling to downwelling irradiance.
Sun Glint
Specular reflectance of sunlight from the water surface that
makes it impossible to interpret or process water column and
substrate/benthic cover information from the data.
Supervised Classification
Image processing approach used to group pixels with a similar
spectral signature as these are assumed to be the same land-cover
class.
Suspended Sediment
Sediment particles that are floating in suspension (as opposed
to dissolved) in the water column.
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T
Technical Officer
The person who does all the real work
Temporal Dimensions
The time at which a sensor overflies a location to collect
an image and/or repeat frequency of image acquisition.
Thematic Map
A map product derived by classifiying each image pixel into
a single category or theme to represent a surface cover feature.
Tripton
The non-organic component or material found in the water column,
i.e. total inorganic matter concentration.
Total Suspended Inorganic Material (TSM)
Tripton = TSM, is the non-organic fraction of the suspended
load within the water column.
U
Underwater Acoustic
An active sensor mounted on boats and used to map bathymetry.
Underwater-Light-Climate
A set of measurements defining the scattering and absorption
controls in the water column.
Upwelling Irradiance
A measurement taken with the sensor head pointing down to
capture incident direct and diffuse light over all directions.
Unsupervised Classification
A mapping approach used for per-pixel classification in image
processing systems which groups pixels automatically based
on their spectral reflectance signature. The analyst then
labels the classes.
User Accuracy
A term used to define the level of accuracy of an image based
map of surface cover types, where select locations are compared
to reference data that the map user has. If 100 pixels are
selected by the map user and compared to the actual ground
cover class and 80 of those are classified correctly, the
user's accuracy is 80%.
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V
Validation
The process used to compare image based estimates or map categories
to some form of reference data to calculate their accuracy.
W
Water Clarity
A subjective term used to verbally describe total attenuation
of sunlight in a water column. This can also be represented
by Secchi-depth and quantified as the diffuse attenuation
coefficient.
Water Roughness
The state of the water surface which is a result of increased
currents and wind. If no current and/or wind then water surface
is flat and smooth.
Wavelength
The distance between peaks or troughs in the electric and
magnetic field of EMR. It is sued to differentiate light with
different energy levels, ie. high energy = short wavelength
blue light and low energy = long wavelength IR lightt
Water Quality Parameters
Biological and physical properties of the water column that
have been adopted by scientific and management agencies as
indicative of the condition of a water body, e.g. Secchi depth,
chlorophyll and total suspended sediment concentration.
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