IFMP Authorized Surveying Officers Certification cheat sheet

Chart datum is the low-water reference to which depths on a nautical chart are reduced; soundings are depths below datum, heights above datum are positive upward.

True bearing is measured clockwise from true north (000°–360°); magnetic bearing differs from true by magnetic variation, and compass bearing differs from magnetic by deviation.

A fix is a position determined by observation; dead reckoning (DR) advances the last fix using course and speed through the water without external position input.

Estimated position (EP) combines DR with at least one line of position or environmental factor; it is less reliable than a fix.

A line of position (LOP) is a locus of points where the observer has a constant measured value; two intersecting LOPs give a fix, and three enable a cocked-hat assessment.

Horizontal datum (e.g., WGS84) defines the coordinate reference for positions; vertical datum (e.g., LAT, MSL) defines the reference for depths and heights; the two are independent.

Scale 1:N means one unit on the survey product represents N units on the ground; larger scale (smaller N) shows more detail over a smaller area.

Positional accuracy is normally stated as a radius of uncertainty at a stated confidence (e.g., 95%); precision describes repeatability, not closeness to truth.

Territorial sea extends up to 12 nautical miles from the baseline; the contiguous zone extends up to 24 nm; the exclusive economic zone (EEZ) extends up to 200 nm from the baseline.

Baselines are normally the low-water line along the coast (normal baseline); straight baselines may join low-water marks where the coast is deeply indented or fringed by islands.

The continental shelf comprises the seabed and subsoil to 200 nm, extendable to 350 nm under UNCLOS Article 76 criteria using foot-of-slope and sediment-thickness formulae.

Equidistance (median line) is the default method for delimiting overlapping zones between opposite or adjacent states, unless special circumstances require a different result.

Innocent passage through the territorial sea requires continuous and expeditious transit and must not be prejudicial to the peace, good order, or security of the coastal state.

Archipelagic states draw archipelagic baselines joining outermost points of outermost islands, provided the water-to-land ratio and baseline length limits under UNCLOS Part IV are met.

Internal waters lie landward of the baseline; the coastal state exercises full sovereignty there, subject to specific rights of access in certain cases.

Boundary coordinates must reference a stated geodetic datum and ellipsoid; a boundary line defined in one datum cannot be compared with another datum without transformation.

Survey order (e.g., Special, Order 1a/1b, Order 2) sets the maximum allowable total vertical uncertainty (TVU) and horizontal uncertainty; the plan must match the order to the water use.

Line spacing is typically set as a multiple of the water depth (commonly 3–4× depth for systematic bathymetry) and reduced where hazards or critical areas exist.

TVU is commonly expressed as TVU = √(a² + (b·d)²), where d is depth and a, b are order-specific constants; horizontal uncertainty follows an analogous form.

Geodetic datum transformation requires at least a defined source and target datum plus transformation parameters (e.g., Helmert 7-parameter) or a published grid shift.

A geoid model converts ellipsoidal heights (from GNSS) to orthometric heights; using ellipsoidal heights directly as chart or tidal references introduces systematic error.

Satellite positioning accuracy depends on geometry (HDOP/VDOP), correction service (e.g., RTK, PPP), and multipath environment; a low DOP indicates strong satellite geometry.

Coverage must include the full area of interest plus a buffer sufficient to confirm that no uncharted hazards exist at the survey boundary.

Tidal reduction requires observed or predicted water levels at the time of sounding; the reduction surface must be documented, including any co-tidal or zoning assumptions.

Sound velocity in water varies with temperature, salinity, and pressure (depth); an uncorrected sound speed profile produces systematic depth bias.

Multibeam echosounders (MBES) measure swath coverage across track; the swath width depends on depth and beam angle, and outer beams generally have lower quality.

Single beam transducers respond to the first return above threshold; in steep or soft terrain the true bottom may be shallower than the detected return.

Side-scan sonar provides imagery of seabed texture and contacts but does not by itself give reliable depth; it is used alongside vertical echosounders.

Tide gauges must be referenced to a stable benchmark and to chart datum; tide station records are required to reduce soundings to datum.

The vertical reference for bathymetry (e.g., LAT, MLLW, MSL) must be stated in the survey report; mixing references without conversion corrupts the depth model.

Overlap between adjacent survey lines confirms coverage and allows cross-checking of depth consistency; gaps in overlap are coverage gaps.

Raw data (navigation, soundings, attitude, sound speed) must be retained unmodified so that processing steps can be audited and repeated.

Transducer draft, sound speed at the face, and latency (time offset between position and depth) are the primary MBES calibration parameters; a patch test estimates them.

A patch test typically uses a line set: a straight line over a slope for latency, a line over a feature for roll, and reciprocal lines for pitch and heading.

GNSS antenna offset (lever arm) from the transducer must be measured in the vessel frame and entered with the correct sign; an unmodeled lever arm creates position bias that grows with vessel motion.

Motion sensor (IMU) lever arm and alignment must be calibrated; unmodeled roll, pitch, or heave produces depth error that increases with beam angle and distance from the sensor.

Bar checks and sound speed profiles should be taken at the start, end, and at intervals during the survey, and whenever conditions change.

Echosounder calibration should be verified against a known reference (e.g., a bar or a surveyed target); a constant offset is a bias, not random error.

Instrument drift and offset detection requires repeat observations of a stable reference; documenting calibration dates and results supports traceability.

Antenna height and geoid model choice must be consistent with the vertical datum used for the final product.

Soundings are reduced to chart datum by subtracting the tidal reduction from the measured depth; the reduction must be consistent across the survey area.

Outlier detection uses statistical filters and visual inspection; spikes that are shallower than surrounding depths are the most safety-critical to resolve.

Cross-line and cross-check analysis compares overlapping data; residuals exceeding the order's uncertainty budget indicate a problem to be corrected.

Total propagated uncertainty (TPU) combines measurement, positioning, motion, and sound speed uncertainties; it is used to decide whether data meet the required order.

Horizontal and vertical datum transformations must be applied consistently to all datasets before merging; mixed-datum merges produce apparent offsets.

Data thinning (e.g., shoal-biased selection) retains the shallowest significant sounding in each cell; this preserves safety while reducing volume.

A quality control record should document the checks performed, the results, and any rejected data; an undocumented correction cannot be validated.

Validation against independent data (e.g., check lines, a different sensor, or known features) is stronger evidence than internal consistency alone.

Chart symbology and depth units must match the chart's stated datum and unit (meters or fathoms/feet); a unit error is a safety-critical defect.

Depths on charts are generally shown to a defined rounding rule (e.g., shoal-biased rounding) so that displayed depths do not overstate available water.

A survey report should state the survey order, datum, equipment, calibration results, coverage, and any limitations or gaps.

Deliverables typically include the digital bathymetric model, the sounding dataset, metadata, and the survey report; each must reference the same datum and units.

Chart updates (e.g., Notice to Mariners) require an identified source, date, and authority; unsourced changes must not be applied.

Metadata should record the coordinate reference system, vertical datum, units, resolution, and processing history so the product can be reused correctly.

Notices to mariners and chart corrections must distinguish permanent changes from temporary or preliminary information.

A vessel safety plan should identify man-overboard, fire, abandon-ship, and medical procedures, with assigned roles and muster points.

Weather and sea-state limits should be defined before operations; data quality degrades and safety risk rises beyond the defined limits.

Personal protective equipment (e.g., life jackets, helmets, hearing protection) is required where the risk assessment identifies a hazard.

Environmental controls include preventing fuel and oil discharge, managing waste, and avoiding disturbance of protected habitats or species.

A pre-survey risk assessment should identify hazards (traffic, shallow water, weather, equipment failure) and the controls applied to each.

Communication and reporting: incidents, near misses, and equipment failures should be recorded and reported through the defined chain.

Vessel traffic and exclusion zones must be observed; survey operations in channels require coordination with port authorities.

Surveyors must hold the required certification and operate within its scope; performing work outside the certification scope is a compliance failure.

Data and reports must be accurate and not misleading; knowingly submitting unverified or altered data is a serious professional and legal breach.

Client confidentiality and data ownership should be defined in the contract; survey data may be subject to national security or proprietary restrictions.

National hydrographic offices and maritime authorities set charting standards and datum conventions; products must conform to the applicable standard.

Records must be retained for the period required by the contract or regulation, and retained data must remain readable and traceable.

Conflicts of interest and gifts or inducements that could affect survey judgments must be disclosed and avoided.

Surveyors should report hazards to navigation to the relevant authority promptly, even when not contractually required.