Glossary

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Glossary

Terminology commonly used in CARIS applications.

altitude

The height of the side scan sonar transducer above the sea floor. The transducer is typically mounted on a towed body or the surface vessel, but can also be mounted on an ROV or AUV.

Angle Varying Gain (AVG)

Angle-Varying Gain (AVG) correction removes the angular response of sediment from the imagery, normalizing the mean angular intensities, ping-by-ping, with a moving average filter.

Area

The actual area of a shape, in the units of measurement of the map.

Aspect

Individual azimuthal map projections are divided into three aspects:

• the polar aspect which is tangent at the pole

• the equatorial aspect which is tangent at the equator

• the oblique aspect which is tangent anywhere else

Attitude Data

Commonly used to refer to the orientation of the vessel in three dimensions as represented by the Gyro, Heave, Pitch, and Roll sensors. The Attitude Editor displays this data as well as other sensors that consists of simple “time vs. sensor value” data.

Azimuth

The angle, measured in degrees, between a base line radiating from a centre point and another line radiating from the same point. Normally, the base line points north, and degrees are measured clockwise from the base line.

background data

Georeferenced vector and raster data providing visual context to the bathymetry and side scan data being processed. Examples include CARIS files, BSB raster charts, GeoTIFF orthophotos, S-57 electronic chart data.

backscatter

Intensity of sounding returns collected by swath multibeam sounding systems. Backscatter data creates an image of the sea floor that can indicate the bottom type.

BAG

The Bathymetric Attributed Grid (BAG) is an open-source binary file format for transferring gridded bathymetry and uncertainty values between software applications and agencies. The file contains five elements: metadata (in XML format), elevation, uncertainty, tracking, and certification. For more information on BAG, go to http://www.opennavsurf.org/.

beam

A single depth measurement is produced from a beam. Many beams make up a profile or ping.

Beam Averaged

A single backscatter return value (intensity, dB) is logged with each beam, taken as an average intensity centred on the bottom detect of the entire time series to produce an image of the sea floor. The intensity for each beam can be directly georeferenced using the positioned beam footprint, but spatial resolution is lost by reducing the full time series to a single value.

Beam Pattern Correction

Beam pattern correction uniformly removes along-track banding inherent to the sonar beam. This effect is produced by each transducer uniquely.

Beam pattern correction relies on a user-generated beam pattern file to identify and remove this effect.

cable out

Length of cable (tow wire) deployed from a towpoint to the towfish. Used in the calculation of lay back.

CARIS file

Now called CARIS map format, this records vector map data features such as lines, symbols, text, soundings, etc. It consists of a set of files.

CATZOC

The zone of confidence (CATZOC) attribute. The CATZOC attribute is part of the S-57 Quality of Data (M_QUAL) object class. It indicates that data meets the minimum criteria for sea floor coverage, and position and depth accuracy as defined by the attribute classification structure. There are five CATZOC classifications: A1, A2, B, C, and D.

Conformality

A map projection is conformal when at any point the scale is the same in every direction. Therefore meridians and parallels intersect at right angles and the shapes of very small areas and angles with very short sides are preserved. The size of most areas, however, is distorted.

contacts

Point and line features identified in side scan sonar data. Attributes describing the location, size, and description or the target are recorded. Image snapshots are also generated.

coverage and surface

A coverage is a digital representation of some time/space-varying phenomenon within a bounded space. A surface is a coverage with defined values at every spatial location within the surface boundary.

Not all coverages are surfaces. A point cloud is a type of coverage, but is not a surface. CARIS has 3 types of coverage that can be used to build surface models: the raster, the TIN and the Variable Resolution surface.

See Representation of coverage types for an illustration of these types.

CSAR

Acronym for CARIS Spatial ARchive: a means of storing high-volume grid and point bathymetric data. Surfaces and mosaics created in HIPS and SIPS are saved in CSAR format.

CSAR files display differently from other file types in that their data structures are stored and multiple levels of resolution. With this structure, data in a data set is always available, although it is not always displayed. For example, if viewing a gridded surface that is zoomed out, the surfaces is displayed as a coarse resolution, appearing smooth and lacking in detail. This coarse display will always include the shoalest depths. Zooming in, the appearance of the surface will change as higher resolution data is brought into view. At any point, making a selection of the points on the surface will give the same results whether zoomed in or not.

CSAR data structures are created with a polygon that represents the outer boundaries of the data. This polygon can be edited, re-digitized or removed by selecting the Bounding Polygon layer in the Layers window.

CUBE surface

A Combined Uncertainty and Bathymetry Estimator (CUBE) surface contains multiple hypotheses representing potential depth variances on the sea floor. As soundings are propagated to nodes, based on distance and uncertainty, a hypothesis is developed. If the there is a significant variation of depth at a node, a new hypotheses is created. A node can contain more than one hypothesis.

d value

Shows the confidence in the grain size assessment and sediment analysis completed by GeoCoder. Smaller values indicate more confidence in the assessment, with values below 0.5 being very good and values above 1.0 being potentially inconclusive. Appears when using Advanced Sediment Analysis.

day

A day for which there is survey data. Expressed as a Julian day.

delta draft

A “time vs. delta-draft” data structure that can be loaded into HIPS and used to model the dynamic squat and lift of the vessel. Also used to store the recorded depth of towfish and ROV/AUV mounted multibeam sonars.

Despeckle

Despeckling uses a calculated value based on neighbouring intensity levels to replace the current pixel’s intensity if it is outside the specified range. The value calculated from the neighbouring intensities can be derived by one of two methods mean or median.

Developable surface

A developable surface is a simple geometric form capable of being flattened without stretching. Many map projects can then be grouped by a particular developable surface: cylinder, cone, or plane.

Direction

The angle between two points (azimuth, bearing, etc.).

disambiguation

The process in CUBE of selecting one hypothesis over other hypotheses to represent the surface. Hypotheses can be selected or “nominated” by density, locale, locale and density, or by the nearest value to a previous CUBE Surface.

Distance

The actual distance between two points, in the units of measurement of the map.

DpTPU

Depth Total Propagated Uncertainty. The difference between the observed or computed depth value of a sounding and its true depth value (at a 95% confidence level).

ellipsoid

The ellipsoid and datum to which logged positions in the survey refer must be stored in the HIPS vessel file, regardless of whether projection coordinates or geographic coordinates are stored in the logged file. Any ellipsoid may be used, so long as it is defined in the file referenced by the environment variable uslXdatum.

ENC

Electronic Navigational Chart

Equal areas

A map projection is equal area if every part, as well as the whole, has the same area as the corresponding part on the Earth, at the same reduced scale. No flat map can be both equal area and conformal.

Equidistant

Equidistant maps show true distances only from the centre of the projection or along a special set of lines. No flat map can be both equidistant and equal area.

field sheet

A collection of data products, within a defined geographic area, derived from the processed bathymetry and side scan data. Field sheets were used in version of HIPS and SIPS prior to 9.0.

Example products included BASE surfaces, mosaics, tiles, selected soundings, and contours. These are now created and edited directly in HIPS.

filtering

The process of detecting outliers in the data and setting the status flags to Rejected. Data points are not removed from the HIPS/SIPS format.

frequency

Number of acoustic waves produced per second (Hz).

gain

A measure of increase in amplitude of a signal.

Gain Correction

Gain Correction adjusts signal intensities using independent port and starboard Gain factor settings. Gain correction can also be applied uniformly to both sides.

gamma

An advanced GeoCoder parameter indicating the spectral exponent of bottom relief.

Generic Data Parser

A program for converting recorded ASCII data sources into the HIPS/SIPS format. New survey lines can be generated for single beam bathymetry, or the program can update a sensor within an existing HIPS or SIPS project.

GPS Tide

Instantaneous water level height above the sounding datum derived from the observed GPS ellipsoid heights of the navigation antenna. Reduced for sensor offsets, vessel motion, known sounding datum height above the ellipsoid, and other parameters.

grain size

An advanced GeoCoder parameter indicating the size of a particle in phi.

Graticule

The graticule is the spherical coordinate system based on lines of latitude and longitude.

Great circle

A circle formed on the surface of a sphere by a plane that passes through the centre of the sphere. The equator, each meridian, and each other full circumference of the Earth forms a great circle. The arc of a great circle shows the shortest distance between points on the surface of the Earth.

GSF

Generic Sensor Format - a file format used for storing bathymetry data.

holiday

Formed when enough significant data gaps are clustered together within a specified radius.

HOB

The Hydrographic Object Binary (HOB) file is a spatially referenced dataset that is used to support the internal structure of S-57 data in CARIS products. The HOB file does not require a CARIS vector map and contains the point, line, and area geometry for hydrographic objects.

HTF

Hydrographic Transfer Format

HVF

HIPS Vessel File. A vessel configuration file in XML format that consists of a list of sensors with their physical and calibration measured offsets, plus any error values. These are applied to the observed data during processing. The HVF supersedes the Vessel Configuration File (VCF).

hypothesis

A representation of depth in a surface. The hypotheses that are displayed in the surface are selected or “nominated” through disambiguation. Hypotheses that were not selected remain as alternative hypotheses and can be nominated in the Subset Editor.

HzTPU

Horizontal Total Propagated Uncertainty. The difference between the observed or computed position value of a sounding and its true position value (at a 95% confidence level).

index contour

A contour line accentuated by a heavier line weight to distinguish it from intermediate contour lines. Index contours are usually shown as every fifth contour with their assigned values, to facilitate reading elevations.

interlaced backscatter

Scattering of the acoustic energy (or acoustic impedance) that occurs at the sediment-water interface where the sea floor reflects and scatters the incident acoustic energy.

Kirchhoff backscatter

Scattering of acoustic energy due to sea floor roughness.

LADS

Laser Airborne Depth Sounder (LADS) is a lidar system developed by Tenix Corporation.

layback

If a towed sensor is used during a survey, the position of that sensor can be calculated as a horizontal “layback” from the position of the towing vehicle. The sensor layback is computed from the tow wire length and sensor depth.

LIDAR

Light Detection And Ranging. Lidar uses laser technology to calculate bathymetry.

line

A single pass of the survey vessel over some or all of the area being surveyed, during which time referenced sensor data is continuously collected. Often the line is approximately straight.

lineage

The processing history of a CSAR surface. Can be viewed from the Lineage field in the Properties window for a selected surface.

Linear scale

Linear scale is the relation between a distance on a map and the corresponding distance on the Earth. Scale varies from place to place on every map. The degree of variation depends on the projection used in making the map.

loss

An advanced GeoCoder parameter measuring the ratio of the imagined wave number to the real wave number for the sediment.

Map projection

A map projection is a systematic representation of a round body such as the Earth on a flat (plane) surface. Each map projection has specific properties that make it useful for specific purposes.

Merge

The process of calculating final positions and depths for soundings, based on all relevant inputs such as observed depths, navigation information, vessel dynamics such as gyro, heave, pitch and roll, and tide. Merging is carried out after these inputs are loaded and checked.

mosaic

A geo-referenced raster image that is a composite of imagery on one or more survey lines.

object

A point, line or area feature including its spatial information (geometry), feature attributes, and symbology. Also referred to as feature, or feature object.

outliers

Unwanted data resulting, for example, from incorrect sea floor detection.

permeability

An advanced GeoCoder parameter measuring the ability of a material (e.g. rock or sediment) to transmit fluids. A factor in the Biot model.

phi

A unit-less number used to represent particle grain size in sediment analysis.

ping

A single output pulse of a sonar system.

point cloud

A set of vertices in a three-dimensional coordinate system. In HIPS and SIPS these vertices are usually defined by X, Y, and Z coordinates, and represent data in 3-D display.

See Representation of coverage types for an illustration comparing a point cloud to surface types.

porosity

An advanced GeoCoder parameter measuring the fraction of voids in a medium (e.g. rock or sediment), or the water space between grains of sediment. A percentage that is a factor in the Biot model.

profile / swath

A set of soundings, approximately perpendicular to the ship’s track, which is produced by the swath or sweep sonar over an instantaneous or very short time period.

product surface

A shoal-biased surface. Data is down-sampled so that finer details of the sea floor are not visible, but the shoals are still maintained.

Created from finalized surfaces, product surfaces maintain the designated soundings from the finalized surface and can be used to create more cartographically correct contours. The finalized surface is smoothed into a generalized product surface that can be used for building contours, sounding selections and profiles.

project

A survey area with data collected by one or more survey vessels over one or more days.

raster

Raster are made from a matrix of pixels or cells in a grid of columns and rows where each cell has a value such as depth or intensity. Examples of rasters in HIPS and SIPS include gridded surfaces and mosaics, in which the cells contain nodes which carry depth or density data related to a coordinate system.

raw side scan

Time indexed imagery profiles where the across-track scale is time in milliseconds.

Rhumb line

A rhumb line is a line on the surface of the Earth cutting all meridians at the same angle. A rhumb line shows true direction. Parallels and meridians, which also maintain constant true directions, may be considered special cases of the rhumb line. A rhumb line is a straight line on a Mercator projection. A straight rhumb line does not show the shorter distance between points unless the points are on the equator or on the same meridian.

RMS

Root mean square error. Used to measure the magnitude of a varying quantity for example to measure the differences between values predicted by a model or an estimator and the values actually observed.

roughness

An advanced GeoCoder parameter measuring the spectral strength (cm4) of bottom relief at wave number 1. Stronger returns would indicate a rougher bottom.

S-44

S-44 is the international standard developed and maintained by the International Hydrographic Organization (IHO) that sets the minimum standard for hydrographic surveys. The standard classifies surveys into survey orders (Special Order, Orders 1a, 1b, 2) based on an area’s importance for safety of surface navigation.

S-57

S-57 is the international standard developed and maintained by the International Maritime Organization (IMO). It is used by hydrographic data producers to describe how real-world entities are stored digitally for transfer among different computer platforms between the various hydrographic offices.

session

A record of all the data (survey line names, background raster images, surfaces and their properties) that are open in the HIPS and SIPS interface when the session is saved. This enables you to re-open an integrated data set from a previous working session.

Shape

A geometrical figure on a map.

(United States Geological Survey, n.d.)

SHOALS

Scanning Hydrographic Airborne Lidar Survey (SHOALS) is a lidar system owned and operated by the Joint Airborne Lidar Bathymetry Technical Center of Expertise.

side scan

The emission of sonar pulses in a wide angle perpendicular to the sea floor to port and starboard that are received and logged as a time series of intensities in order to form an image. This data is logged separately from the bathymetry data. A swath multibeam system forms two additional receive beams in addition to the bathymetry profile.

slant range

Raw travel time used to compute sounding depth (accompanied by receive angle).

Slant Range Corrected Side Scan

Time-indexed imagery profiles generated from raw side scan data using the measured altitude of the transducer. The across-track scale is distance in metres.

slice

A subset of a selection in a display window, defined by a bounding box, for example, the 2D slice of the subset loaded in Subset Editor.

sounding

A measured depth of water.

Sounding datum height

Distance from the ellipsoid to the sounding datum.

Sound Velocity Correction

The process of applying rigorous refraction corrections to the raw travel time/angle bathymetry data using recorded sound velocity profiles.

Status Flag

The indicator of the acceptance or rejection of a data point during cleaning.

status indicators

Many dialog boxes have a small box to the right of a value field. If a setting in the field is changed from the default value, the status indicator box for the field changes to grey. Defaults can be restored by clicking on the indicator box and selecting “Reset”.

subset

A rectangular area which encloses some or all of a survey project shown in the Display window. It is used during sounding cleaning to limit the number and extent of soundings being processed during one session.

superselected

A superselected feature is a subset of a selection of multiple features. When a number of features are selected, but the attributes or properties of only one feature can be viewed or acted upon, it is the superselected feature which will be affected. In HIPS and SIPS the superselected feature is coloured light blue in the Display window and other features in the selection are coloured red. In the Selection window, the superselected feature is highlighted.

surface

A grid structure that uses the XY position of specific soundings. For example, depending on the chosen gridding method, a surface can retain the original XY coordinates of the shoalest depths.

A surface is saved as a CSAR file, using the CARIS Spatial ARchive framework. This file contains the data and metadata for the surface.

surface cleaning

A statistical process of detecting bathymetric outliers within an area. A least square polynomial regression algorithm is used.

tiles

A representation of the sea floor consisting of interlocking tiles of varying sizes. Tiles can make large data sets more manageable by subdividing them by user-defined criteria.

Tile positions are defined by a Morton Number scheme. Tiles can carry a variety of attributes generated from the data within the area of the tile.

time series

A series of intensity values (dB) logged with each beam that is added based on the time and range of detection point to assemble a trace similar to a side scan image. Each individual time series is associated with a portion of the bathymetric profile.

This detection method allows for a higher across-track spatial resolution of sea floor features (with spatial frequencies higher than the beam spacing) since a portion of the time series is preserved for each beam.

Time-Varying Gain (TVG)

The attenuation of acoustic energy that occurs due to absorption and spreading as the sonar beam travels back to the receiver, resulting in a non-uniform gain across the swath. Since signal returns are received over a predictable and constant time period, a correction can be used to adjust the signal intensity by applying a non-uniform, time dependent gain.

TIN

A triangulated irregular network (TIN) is a digital terrain model which consists of a series of triangles with the data points as vertices. A TIN uses the actual elevation for each data point.

tortuosity

A unit-less advanced GeoCoder parameter indicating the characteristic of flow through porous media, or twisting of the pore space. This is a factor in the Biot model, and smaller numbers (1 is the minimum value) indicate a straighter path of potential flow, while higher numbers would have a more twisted path.

total backscatter

Combination of backscatter that occurs due to the interface change (Interface Backscatter), sediment heterogeneities (Volume Backscatter), and roughness of the sediment (Kirchhoff Backscatter).

TPU

Total Propagated Uncertainty. TPU is derived from a combination of all individual error sources and is used to calculate horizontal and vertical uncertainties for soundings.

vector

Vector data refers to point and line features in a digital map or chart.

It also refers to the direct connection between two points, either given as two sets of coordinate (points), by direction and distance from one given set of coordinates, or a point in a vector space defined by one set of coordinates relative to the origin of a coordinate system.