Atmospheric remote sensing toolkit

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Glossary

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# Glossary

A B C D E F G H I JK L M N O P Q R S T U V WXYZ

# A

#### Above-ground biomass

All living biomass above the soil including stem, stump, branches, bark, seeds, and foliage.
http://www.mfe.govt.nz/issues/climate/lucas/glossary/glossary.html

#### Absorbed photosynthetically active radiation (PAR)

Is the amount of the Photosynthetically Active Radiation (PAR) that is absorbed through a photosynthetic medium (e.g. vegetation canopy, ocean).

#### 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 fires

An active, burning fire demonstrating thermal anomalies.

#### Active sensors

Sensors with their own source of radiation, e.g. laser altimeters, imaging radar and acoustic systems. For more information see passive and active imaging systems.

#### Accuracy

Is the degree of conformity of a measured or calculated quantity to its actual (true) value. Click for more information on accuracy and error assessment (opens in new window).

#### Acoustic

See Underwater acoustic.

#### Adjusted accuracy

An accuracy value modified for the influence of a particular factor or variable.

#### Aerosols

A suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution and smog (Wikipedia).

#### Aerosol optical depth/ thickness

A dimensionless parameter that describes the degree to which aerosol prevents the transmission of light.

#### Aerosol particle mass concentration

A class of parameters that describe the mass concentration, or density, of an aerosol – i.e. the columnar aerosol mass concentration (μgm/cm2) is the total aerosol mass in a vertical column of atmosphere.

#### Aerosol particle size distribution

A class of parameters that describe the size of an aerosol – either directly measured (i.e. particle diameter in µm) or calculated (i.e. Angstrom exponent).

#### Aerosol species

Several schemes to classify aerosol determined by emitting source, particle size or chemical compound.

#### Aerosol structure in profile

An image of the vertical profile of aerosol in the atmosphere (in this context usually a product from the CALIPSO satellite).

#### Airborne laser

Active 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

#### Airmass stability indices

A class of measurements describing the air-mass stability of the troposphere involving temperature and moisture retrievals.

#### Air temperature profile

A calculated representation of the air temperature with varying methods for indicating the change in temperature due height depending on the instrument used for retrieval.

#### Air-water interface

Ocean-atmosphere (gas-liquid) boundary which alters the direction and magnitude of sunlight

#### Air-water interface correction

Correction of pixel values for the influences such as surface glint or surface roughness. Click for more information (opens in new window).

#### Airborne laser

Active 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.

#### Albedo

The ratio of the radiation reflected from an object to the total amount incident upon it, for a particular portion of the spectrum.

#### 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

#### ALOS

The Advanced Land Observing Satellite (ALOS) is a Japanese satellite launched in 2006 equipped with three sensors: PRISM, a panchromatic radiometer; AVNIR-2 a visible and near-infrared radiometer; and PALSAR, a phased array type L-band Synthetic Aperture Radar.

#### Analytical modeling

Image processing approach used to estimate biophysical properties (e.g. total suspended sediment concentration) by applying radiative transfer equations to image data.

#### Angstrom exponent

A calculated parameter that expresses the spectral dependence of aerosol optical thickness with the wavelength of incident light providing additional information on the particle size (the larger the exponent, the smaller the particle size).

#### AOPs

Apparent optical properties of water - those dependent on the strength and direction of incident sunlight, e.g. reflectance.

Atmospheric correction

Image 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. Click for more information (opens in new window).

#### Atmospheric environments

The envelope of air surrounding the Earth, including its interfaces and interactions with the Earth's solid or liquid surface. Go to atmospheric remote sensing toolkit.

#### Atmospheric motion

The wind speed and direction – usually surface winds in the remote sensing context.

#### Atmospheric water vapour

A derived measure of the concentration of water vapour in a column of atmosphere – several parameters exist depending on spectral capability of the instrument (or data amalgamation from instruments) from which the parameter was derived.

#### Attenuation

Distortion of true reflectance or radiance levels due to absorption and scattering effects.

#### Attenuation coefficient

Describes the amount of absorption and scattering of a particularly wavelength of light through the water column.

#### AVNIR

AVNIR (Advanced Visible and Near Infrared Radiometer) on the Advanced Earth Observation Satellite (ADEOS) was launched in August 1996. AVNIR was succeeded by AVNIR-2 on ALOS launched in 2006. AVNIR-2 is a visible and near infrared radiometer for observing land and coastal zones. Spatial Resolution: 10m Swath Width: 70km.

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# 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.

#### Bank full width

(1) bank full width; (2) elevation difference between the streambed and the top of the lowest bank; (3) slope of the lowest bank; and (4) slope in the area of the top of the lowest bank.

#### Bank condition

The bank condition indicator is an assessment of the ‘ideal’ stability of the bank in relation to numerous physical identifies.

#### Bare ground cover

Bare land surface without photosynthetic or non-photosynthetic vegetation.

#### Basal area

The cross-sectional area of a tree trunk.

#### Bathymetry

Depth of the water column to substrate, measured relative to a specified height datum.

#### Benthic community

Defined as an assemblage of stony coral and / or other conspicuous benthic populations which can co-exist on reefal or non-reefal substrates (Done 1999).

#### Benthic community scale

See reef scales.

#### 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.

#### Bi-directional reflectance correction (BRDF correction)

BRDF (*) causes non-uniform illumination across a scene, hot spots. Image data are internally inconsistent and unable to be processed. By applying a mathematical transformation the BRDF effect can be removed. (*BRDF = Bi-Directional Reflectance Distribution Function). Click for more information (opens in new window).

#### 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

#### CASI

Compact Airborne Spectrographic Imager - an airborne hyperspectral imaging system.

#### Calibration

A process used to initialize a mathematical model to certain measured conditions.

#### Canopy overhang

Canopy overhanging the streambed.

#### Canopy weeds

Non-native tree, shrub or ground cover.

#### CDOM

Coloured dissolved organic material

#### CH4

Methane – chemical formula CH4

#### Change and trend detection

Detection of changes in a biophysical variable, parameter or thematic value through time.

#### Chlorophyll A

Primary pigment used to capture sunlight for use in a plant's photosystem during photosynthesis.

#### Chlorophyll concentration

A measure of the chlorophyll photosynthetic pigment on the ocean surface (commonly used as an indicator of phytoplankton).

#### Cloud effective radius

A calculation using cloud droplet radii describing the scattering of light by cloud droplets.

#### Cloud mask/fraction

Cloud mask is used to remove areas obstructed by cloud between the surface and the satellite. Cloud fraction provides a percentage of the image covered by cloud.

#### Cloud optical thickness

A dimensionless derived parameter that describes the degree to which cloud droplets prevents the transmission of light.

#### Cloud phase

A derived measure Indicating the phase of the cloud water content – water, ice or both (mixed).

#### Cloud structure in profile

An image of the vertical profile of clouds (in this context usually a product from the CloudSat satellite).

#### Cloud top pressure

A derived measure of the air pressure for the cloud skin as viewed by a satellite.

#### Cloud top temperature

A brightness temperature measure of the cloud skin as viewed by a satellite.

#### CO2

Carbon dioxide – chemical formula CO2

#### 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

#### Coastline

Boundary between land and sea.

#### Coloured dissolved organic matter (CDOM) concentration

The concentration of the optically measurable component of the dissolved organic matter in water.

#### Composition and biomass

Composition: composition of species in the variable of interest. Biomass: mass of living organisms (either a particular species or all species in a community) in a given area or ecosystem.

#### Continuous map

A map showing spatial variation in a quantitative property, e.g. water depth, without grouping it into discrete thematic classes.

#### Control points

see Natural control points

#### Coordinate system

A reference system used to define location in relation to a set origin point, i.e. [x, y, z]

#### Coral bleaching severity – low, moderate, severe

Severity levels of coral bleaching used by the Great Barrier Reef Marine Park Authority. Click for more information (opens in new window).

#### Coral habitat

An area with suitable conditions to allow the groath and maintenance of coral reefs.

#### Coral Point Count Excel

The National Coral Reef Institute (NCRI) Coral Point Count with Excel extensions (CPCe) program is Windows-based software (PC use only) that provides a tool for the determination of coral cover using transect photographs. Click for more information (opens in new window).

#### Cover type

A type of living or non-living feature, commonly occurring over substrate.

#### Crown and gap widths

Crown width (or diameter) is the width of a single tree canopy. Gap width is the distance between tree crowns.

#### Cyanobacterial bloom

A kind of algal bloom occurring when cyanobacteria grows exuberantly. Can cover the water surface and cause water to become cloudy.

#### Cyanobacterial blooms (other then Lyngbya)

A kind of algal bloom occurring when cyanobacteria (not of the Lyngbya genus) grows exuberantly.

#### Cyclone/Hurricane impact

A disturbance to either natural or built environment caused by a cyclone or hurricane.

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# D

#### Dark pixel correction

A simple ad hoc method for atmospheric correction. Click for more information (opens in new window).

#### Datum

An origin point or surface for vertical or horizontal coordinates.

#### Depth correction

Correcting reflectance for attenuation effects of the water column. Click for more information (opens in new window).

#### 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

#### Droplet radius

The radius of a liquid water cloud droplet.

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# E

#### 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.

#### Elevation

The vertical distance between a standard reference point, such as sea level, and the top of an object or point on the Earth, such as a mountain.

#### Emitted longwave radiance

Longwave radiation emitted from a surface. See also radiance.

#### 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.

#### Eo-1

NASA satellite - experimental platform for Hyperion and ALI

#### Error matrix

A table for comparing the mapped value or category in an image to a reference value obtained from field survey. Click for more information (opens in new window).

#### Euphotic depth

Water depth where photosynthetic available radiation (PAR) is 1% of its surface value, a measure of water clarity.

#### Event based mapping

Mapping a disturbance created by an event such as vessel grounding, cyclone impact or flood.

#### Extent

May refer to the dimensions of a satellite scene or the desired area of the mapping application. Click for more information.

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# 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.

#### Fire fuel load

The total amount of combustible material per unit area.

#### Fire scars

Area of land surface visibly disturbed by burning.

#### Foliage projected cover

Proportion of the ground covered by the vertical projection of the vegetation.

#### Foliar chemistry

The chemical composition of foliage.

#### Foliar moisture content

Foliage water content, often expressed as a percentage of the dry mass.

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# G

#### Geometric correction

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. Also known as georeferencing. Click for more information (opens in new window).

#### Geomorphic zone scale

See reef scales.

#### Georeferenced photo transect surveys

A field survey where photos are taken and registered to a coordinate. Often used for accuracy assessment. Click for more information (opens in new window).

#### Georeferencing

See geometric correction

#### Grain size

Refers to the diameter of a particle e.g. snow, sediment or rock.

#### 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 control points

see Natural control points

#### Ground height

Insert text - See also stereo images.

#### Ground resolution element (GRE)

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.

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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.

#### Hemispherical photography

Using fisheye photography to characterise canopy cover and canopy gaps. Click for more information (opens in new window).

#### Hydro-optical properties

Properties that affect the behaviour of light in the water column e.g. reflectance, attenuation.

#### 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. See http://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). Click for more information on multispectral and hyperspectral imaging systems.

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# 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. Click for more information (opens in new window).

#### 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.

#### In-stream large wood

Location and density of in-stream large wood, including total volume of wood in and above the water.

#### Irradiance reflectance

A ratio of reflected sunlight measured over all directions to incident sunlight measured over all directions.

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# JK

#### Kd

Vertical diffuse attenuation coefficient - an estimate of the amount of light attenuated by water per unit depth.

#### Kappa accuracy

The adjusted overall accuracy indicates the extent to which the percentage correct values are due to “true” agreement versus “chance” agreement (Lillesand et al., 2008). Kappa accuracy, or k^ (k-hat), is the actual agreement between reference data and the image based classification, corrected for the chance agreement between the reference and results of a random classification (Congalton 1991; Ma and Redmond 1995). See also accuracy and overall accuracy. Click for more information (opens in new window).

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# L

#### Land cover

Describes the earth’s surface e.g. vegetated, asphalt, bare, water, snow/ice.

#### Land use

Describes the human modification of the land surface e.g. urban, agriculture.

#### Landsat Thematic Mapper (TM) /Enhanced Thematic Mapper (ETM)

General purpose multispectral, moderate spatial resolution imaging satellite sensors that have operate since the mid 1980s (TM) and April 1999 (ETM).

#### Leaf area index

A ratio of leaf area per unit of ground area. An important parameter used in remote sensing to quantify many biological and physical processes such as primary productivity, plant respiration, transpiration, photosynthesis and nutrient cycles.

#### 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.

#### Longitudinal continuity

A measure of streamside vegetation continuity.

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# M

#### Mangroves

A salt-tolerant plant that lives in the intertidal zone.

#### Manual delineation and labelling

Manual selection or digitising of mapping classes, either pre- or post-classification. Click for more information (opens in new window).

#### Marine environment

Abiotic and biotic features below the high-tide limit to the sea-floor. Go to terrestrial remote sensing toolkit.

#### 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

#### Mineralogy

The study of minerals; may refer to the chemical structure, physical and optical properties of minerals.

#### Minimum mapping unit

The smallest spatial unit to be shown on a map.

#### MODIS

Moderate Resolution Imaging Spectrometer - See http://modis.gsfc.nasa.gov/

#### Moisture

May refer to the presence of water or the water content.

#### 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.

#### Multispectral

An image data collection system where reflected or emitted energy is measured in less than 10 broad spectral bands. (cf. hyperspectral). Click for more information on multispectral and hyperspectral imaging systems.

#### Multi-temporal

Data that has been collected for the same area over a series of successive dates.

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# N

Nitrogen – chemical formula N

#### N2O

Nitrous oxide – chemical formula N2O

#### Natural 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.

#### Near infra-red (NIR)

The non-visible 700-1000nm portion of the EMR spectrum

#### Normalised Difference Vegetation Index (NDVI)

A normalised ratio transformation using the red and NIR pixel values which is sensitive to vegetation cover.

#### Number of large trees

Density of large trees in riparian zone compared to minimum DBH for EVC benchmark (*). Large trees are graded healthy/unhealthy (if level of insect attack, mistletoe, or missing foliage is significantly noticeable). Only indigenous species are assessed. The number of healthy large trees is divided by the total number of large trees. Score is determined based on this number. (* DBH = Diameter at Breast Height, EVC = Ecological Vegetation Classes).

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# O

Oxygen – chemical formula, O – commonly in its most stable form O2

#### O2

Oxygen – chemical formula O2

#### O3

Ozone – chemical formula O3

#### 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. Click for more information (opens in new window).

#### Oil spill

The release of liquid petroleum products into the environment. Often refers to the release of oil into a marine environment from an oil tanker.

#### Operational but cost-prohibitive

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.

#### Optical depth / thickness

The degree to which the atmosphere or an optical material prevents light from passing through it. The depth at which passive remote sensing can retrieve reliable information.

#### 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.

#### Other biophysical properties

Insert text

#### 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% See also accuracy. Click for more information (opens in new window).

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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.

#### Particle mass concentration

See aerosol particle mass concentration

#### Particle size distribution

The range of particle sizes in a material e.g. rocks, soils, aerosols. See also aerosol particle size distribution.

#### Passive sensors

Imaging sensors that measure reflected sunlight or emitted thermal energy. For more information see passive and active imaging systems.

#### 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.

#### Photosynthetically active radiation (PAR)

Radiation between 400 and 700 nm used by photosynthetic organisms in the photosynthetic process.

#### Physics-based correction

A physics-based approach uses complex mathematical relationships or equations to solve for a particular parameter. E.g. radiative transfer equation, bidirectional reflectance and distribution function. Click for more information (opens in new window).

#### 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).

#### Plant projective cover

A measure of the level of light infiltration through the canopy.

#### Platform type

The vehicle on which a sensor is mounted, e.g. satellite, aircraft, boat, balloon, person.

#### Positional accuracy

The difference between a measured coordinate and its true location or a reference value for that location.

#### Post classification

Steps that may be applied to digital image files after classification e.g. smoothing, change detection. Click for more information (opens in new window).

#### 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.

#### Presence/absence

Mapping method that identifies the presence or absence of a desired parameter.

#### 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%. Click for more information (opens in new window).

#### 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. See http://www.digitalglobe.com/index.php/85/QuickBird

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# 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. Click for more information (opens in new window).

#### 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. Click for more information (opens in new window).

#### Radiometric resolution

Smallest difference in reflected light able to be detected by a sensor and its dynamic range. Click for more information.

#### Radio-sonde data

Vertical profile through the atmosphere of temperature and humidity, used for atmospheric correction.

#### Rain rate

A measure of the amount of rainfall in a unit of time (e.g. mm/hr); describes the rainfall intensity.

#### Random sampling

The random sampling is the preferred scheme due to the statistical properties that result from the random selection of samples. The random sampling is the preferred scheme due to the statistical properties that result from the random selection of samples. See also sampling scheme.

#### Reef patch scale

See reef scales.

#### Reef scale

See reef scales.

#### Reef scales

The spatial scales to which coral reef and seagrass habitats are mapped vary with: patch reef (cm-m); benthic communities (1-10 m); geomorphic zone (10-100 m); reef (100-1000 m) and reef system (1-1000 km). Click for more information (opens in new window).

#### Reef system scale

See reef scales.

#### Reflectance signature

Ratio of upwelling radiance to downwelling irradiance on a target, i.e. its characteristic absorption/reflectance response. Click for more information (opens in new window).

#### 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.

#### Regression analysis

A statistical analysis describing the relationship between two variables. Click for more information (opens in new window).

#### 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.

#### Riparian vegetation

A riparian zone or riparian area is the interface between land and a stream. Plant communities along the river margins are called riparian vegetation, characterized by hydrophilic plants.

#### Riparian zone width

Is determined by considering the plants that are found next to the stream. The extent of the width is given by the presence of plants that are are dependent on the stream for their survival. The riparian zone can include the vegetation on any bars/ benches that exists.

#### River - sediment discharge plume mapping

The mapping of a sediment cloud at a river mouth.

#### Rugosity

A measure of surface roughness commonly used to describe the marine seafloor environment.

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# S

#### Saltmarsh

A coastal saltmarsh is a community of salt-tolerant plants and animals that grow along the upper-intertidal zone (above the mean spring-tide height) of coastal waterways, mainly in temperate regions.

#### Sampling Design

In the context of accuracy assessment it refers to the sampling design is described by: sample unit size, number of samples, spatial distribution of samples, and data collection process at each sample unit (Stehman and Czaplewski 1998; Congalton and Green 1999; Foody et al., 2006). Click for more information (opens in new window).

#### Sampling Number

In the context of accuracy assessment it refers to the number of samples used for the validation process. Click for more information (opens in new window).

#### Sampling Scheme

In the context of accuracy assessment it refers to the spatial distribution of sample units in the study area is determined by sampling schemes.Click for more information (opens in new window).

#### Sampling Unit

Sampling units define the spatial extent of the reference data used to calibrate and validate a map product and its map classes. Sampling units are either: points, or areas (e.g. pixels or cluster of pixels) (Stehman and Czaplewski 1998). Click for more information (opens in new window).

#### 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

#### Seagrass habitats

An ecosystem dominated by seagrass communities.

#### 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.

#### Shallow benthic cover

Living and non-living features covering the substrate at depths shallower than 15-20m

#### Ship grounding

A marine accident involving impact of a ship upon the seafloor.

#### 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.

#### Slope and aspect

Slope describes the gradient or incline of non-horizontal terrain. Aspect is the direction of which the slope faces. See also stereo images.

#### 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. Click for more information.

#### 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. Click for more information.

#### 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. Click for more information.

#### Spectral signature

See reflectance signature.

#### Spectral angle mapping

An image classification approach used to group pixels with similar reflectance signature.

#### Species

A taxanomic rank.

#### Spot Xs

Commercially operated high-moderate spatial resolution (20m) multispectral and panchromatic (5m) satellite imaging sensor. See http://spot5.cnes.fr/gb/programme/programme.htm

#### Striping effects

Artifacts introduced in coastal Landsat sensor scenes due to scanner variations every 16 lines.

#### Stereo images

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#### Structure in profile

See aerosol structure in profile or cloud structure in profile.

#### Stratified sampling

Classified according to various criteria into successive levels or layers. Click for more information (opens in new window).

#### Stratified-random sampling

Assigning random samples evenly across classes. Click for more information (opens in new window).

#### Streambed width

(1) distance from the toe of the bank on one side of the stream to the toe of the bank on the opposite side of the stream; (2) and slope of the toe of the bank.

#### 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. Click for more information (opens in new window).

#### 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. Click for more information (opens in new window).

#### Surface Currents

Ocean currents near the surface.

#### Surface Temperature

Temperature at or near the surface. May refer to sea surface temperature or land surface temperature.

#### Surface Winds

Wind blowing near the surface. Often measured at 10 m above the earth’s surface.

#### Suspended sediment

Sediment particles that are floating in suspension (as opposed to dissolved) in the water column.

#### Suspended sediment concentration

The concentration of sediment suspended in a medium e.g water, air, ice.

#### Systematic error

An error that is not determined by chance but is introduced by an inaccuracy in the system. Systematic errors are predictable and expected. Click for more information (opens in new window).

#### Systematic sampling

Insert text. Click for more information (opens in new window).

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# T

#### Tau accuracy

The Tau accuracy, or Tau coefficient, is similar to Kappa accuracy, and provides an improved adjustment for the chance agreement (Ma and Redmond 1995). In contrast, Kappa accuracy is considered to be over-corrected for the chance agreement (Foody 1992). See also accuracy and overall accuracy. Click for more information (opens in new window).

#### Technical officer

Adresses technical issues that a organisation faces, including research and development.

#### Temporal dimensions

The time at which a sensor overflies a location to collect an image and/or repeat frequency of image acquisition. Click for more information.

#### Terrain height

Height of surface above a datum e.g. above sea level. See also stereo images.

#### Terrestrial environment

Land surface environment, defined as the abiotic and biotic features above the high-tide limit to its boundary layer with the atmosphere. Go to terrestrial remote sensing toolkit.

#### Thematic map

A map product derived by classifiying each image pixel into a single category or theme to represent a surface cover feature.

#### Thickness

See optical depth.

#### Transmissivity

The ratio of the transmitted radiation to the radiation arriving perpendicular to the boundary between two mediums.

#### Tree density

Amount of trees per unit area.

#### Tree height

Height of tree canopy above the ground surface.

#### Trend detection

Identification of patterns of change in a time series. Click for more information (opens in new window).

#### 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.

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# 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. Click for more information (opens in new window).

#### 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%. Click for more information (opens in new window).

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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. - LINK

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# WXYZ

#### 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. Click for more information (opens in new window).

#### Water colour

The colour or spectral signature of water. May be influenced by various biotic and abiotic factors e.g. sediment, phytoplankton bloom.

#### Water equivalent (snow)

Snow water equivalent can be presented in units of kg/m2 or meters of depth of liquid water that would result from melting the snow.

#### Water quality

Can refer to the physical, chemical, or biological characteristics of water.

#### Water vapour

Gas phase of water.

#### 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 light.

#### 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.

#### Wave height

Difference between the wave crest and the wave trough.

#### Worldview 2

Commercially operated very high spatial resolution (46 cm) multispectral and panchromatic satellite imaging sensor. See http://worldview2.digitalglobe.com/

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