PORP cheat sheet

PORTS is a NOAA National Ocean Service program (administered through CO-OPS) that funds, operates, and disseminates real-time coastal observations for safe navigation and environmental decision-making.

Core PORTS product set: real-time water level, currents, wind, air/water temperature, barometric pressure, visibility, waves, and salinity; delivered as observations, predictions, and derived guidance.

Governance layers: federal program office (standards, funding, data policy), regional/local system operators (installation, maintenance), and user groups (harbor pilots, port authorities, Coast Guard) that define requirements.

Requirements-driven design: a PORTS system is scoped by the local user working group's operational thresholds (e.g., channel depth, current limits) before sensor siting is chosen.

Data policy: NOAA observational data are made available openly and without restriction; redistribution by third parties is permitted with attribution to the source.

Performance metrics reported for PORTS include data availability (percent valid per period), timeliness, and accuracy relative to reference sensors.

A system of record: all observations are archived centrally with metadata (station, sensor, datum, units) so historical queries and hindcasts are reproducible.

Stakeholder map: program office, regional association/operator, port authority, pilots, Coast Guard, NWS/NOS partners, academic operators, and the public data consumer.

Water level: acoustic (air) or pressure (submersible) sensors referenced to a fixed orifice; the sensor measures height above a known benchmark, not depth of water in an absolute frame.

Currents: ADCP measures Doppler shift from scatterers in multiple beams; a bottom-mounted upward-looking ADCP profiles the water column, while side-looking units measure a horizontal slice.

Wind: sonic anemometers give 2-axis vector wind with no moving parts; mechanical cup/vane sensors need bearing and cup calibration and are prone to icing and salt fouling.

Barometric pressure: silicon capacitive or vibrating-element sensors; report in hPa or mb and correct to sea level for synoptic comparison.

Temperature: thermistors (water) and platinum RTDs (air) with radiation shields; air sensors require aspirated shields to avoid solar bias.

Visibility: forward-scatter or transmissometer sensors; output in nautical miles or meters, with calibration against local reference visibility and fog climatology.

Waves: bottom pressure or surface buoy accelerometers; significant wave height Hm0 = 4*sqrt(m0) where m0 is the variance of the surface elevation spectrum.

Salinity/conductivity: inductive or electrode cells; report practical salinity (PSS-78) or absolute salinity, and never mix the two in a data stream.

Sampling chain: sensor → datalogger (A/D, averaging, timestamping) → telemetry → central ingest → QC → dissemination; each stage must preserve the timestamp and units.

Averaging windows: water level commonly 1-minute or 6-minute values; winds typically 2-minute or 10-minute means with gust maxima; document the window in metadata.

Telemetry options: cellular (LTE/5G), satellite (GOES, Iridium), spread-spectrum radio, and hardwired/fiber; choose by bandwidth, latency, power budget, and coverage.

GOES DCP: fixed time slots, low bandwidth, one-way; data arrive with latency of minutes and no acknowledgement, so dataloggers must buffer and retransmit.

Timekeeping: GPS-disciplined clocks or NTP; timestamps must be UTC and every record must carry a station and sensor identifier.

Data integrity: checksums/CRC on telemetry frames, sequence numbers to detect gaps, and store-and-forward buffering for outages.

Power budget: solar panel sizing must cover worst-case winter insolation plus depth of discharge margin; batteries sized for consecutive cloudy days.

Redundancy: primary and secondary telemetry paths, dual sensors at critical stations, and local non-volatile logging independent of communications.

Real-time QC is automated and conservative: it flags suspect values rather than deleting them, so downstream users can decide.

Common tests: range (climatological limits), rate-of-change (step/spike), flat-line/stuck sensor, persistence, and inter-sensor comparison (e.g., pressure vs. water level).

Flag conventions: good/valid, suspect, bad/invalid, missing, and estimated; a value may be present but flagged, and flags propagate to derived products.

Outlier logic: a spike test compares a value to the median of neighbors; a step test detects abrupt level shifts inconsistent with physical rates.

Tidal prediction residual check: compare observed water level to predicted tide; large residuals trigger review for storm surge, seiche, or sensor drift.

Metadata QC: missing units, wrong datum, or unverified benchmark invalidate a record regardless of how plausible the numbers look.

Delayed-mode QA/QC is manual review with reference comparisons, benchmark leveling, and sensor histories; results can revise real-time flags.

Data availability target: compute percent valid as (valid records / expected records) × 100 over the reporting period, excluding documented outages.

Datum hierarchy: MLLW is the chart datum for most U.S. waters; MHW, MSL, NAVD88, and station datum are related by published offsets.

Tidal datum definition: MHW and MLLW are computed from a 19-year National Tidal Datum Epoch (NTDE) of hourly heights; the current epoch is 1983–2001.

Datum transfer: short-term (≥1 month) observations are compared to a nearby long-term control station to transfer datums, with error growing as the record shortens.

Mean range = MHW − MLLW; diurnal range = MHHW − MLLW; these differ for mixed and diurnal regimes.

Tide prediction: harmonic analysis fits constituents (M2, S2, N2, K1, O1, etc.) to observed heights; prediction = sum of constituent amplitudes × cos(phase argument).

Residual = observed − predicted; positive residual indicates water above prediction (surge, runoff, seiche).

Water level reduction: heights are reduced to a common datum by subtracting the station datum offset; never mix datums within a product.

Datum updates: when the NTDE is revised, published datum offsets shift; products must state which epoch and datum they reference.

ADCP coordinate frames: beam, instrument, and earth (ENU); current products are normally reported in earth coordinates with declination applied.

Velocity profile: bin size, blanking distance, and number of bins define the profile; side-lobe contamination limits the top bin near the surface.

Current reporting: speed (m/s or knots) and direction (degrees true, direction toward which the current flows, or set/drift); state the convention explicitly.

Tidal current prediction uses harmonic constituents for u and v separately; flood/ebb and slack water are derived from the predicted vector.

Wave spectra: compute from heave/pressure time series; Hm0, peak period Tp, and mean wave direction are standard outputs.

Pressure-based wave sensors must correct for attenuation with depth; the correction grows with wave frequency and sensor depth.

Wind reporting: direction is the direction the wind blows from (meteorological convention), in degrees true; speed in m/s or knots at a stated height (typically 10 m).

Derived quantities: wind stress, wave steepness, and combined wave-current effects must be documented with their formulas in the metadata.

Preventive maintenance cycle: scheduled site visits for sensor cleaning, orifice clearing, desiccant/battery check, and benchmark leveling.

Leveling: water level sensors require differential leveling to a stable benchmark; an unresolved benchmark error propagates directly into reported heights.

Common faults: biofouling on conductivity and optical sensors, ice on anemometers, air bubbles in pressure lines, and cable chafe at the connector.

Troubleshooting order: verify power → verify datalogger clock and program → verify sensor output locally → verify telemetry → verify central ingest.

Stuck-value diagnosis: compare against a co-located or nearby station; a flat line across all sensors points to the logger, not the sensor.

Change control: any sensor swap, relocation, or program change is recorded in the station metadata with effective date and reason.

Spares and calibration: keep calibrated spares and track calibration dates; a sensor out of calibration is a data quality issue even if it reports.

Outage response: document start/end time, cause, and corrective action; availability metrics are computed from these records.

Product classes: observations (measured), predictions (astronomical tide/current), and guidance (derived thresholds for navigation decisions).

Water level products: observed, predicted, and residual; storm surge is the residual above predicted tide, not the total water level.

Currents products: real-time profile, depth-averaged current, and predicted tidal current for the channel.

Meteorological products: wind speed/direction, gusts, pressure, visibility, and air/water temperature for pilot boarding and berthing decisions.

Data formats: tabular/text, XML/JSON web services, and graphical displays; every product states station, units, datum, and timestamp in UTC.

Latency tiers: real-time (minutes), near-real-time, and archived/delayed-mode; users must know which tier a product comes from.

User thresholds: pilots use current speed and visibility limits; port authorities use water level for under-keel clearance; Coast Guard uses conditions for closures.

Metadata and provenance: a product without station, sensor, datum, and QC flag context is not actionable for navigation.

Field work requires a job hazard analysis, a float plan or check-in schedule, and a designated shore contact before departure.

Personal protective equipment for over-water work: PFD, hard hat, gloves, eye protection, and fall protection where required.

Lifting and over-water operations need a spotter, tagged lines, and awareness of vessel traffic; never work alone on a small boat.

Environmental compliance: permits for placing instruments on the seabed, protected-species and habitat review, and avoidance of sensitive benthic areas.

Marine debris and fouling: antifouling coatings and cleaning schedules must comply with local discharge and coating regulations.

Electrical safety: solar/battery systems require fusing, disconnects, and lockout/tagout before servicing; DC arcs are a real hazard.

Weather go/no-go: small-craft advisory, lightning, and sea-state thresholds are defined in the operations plan, not decided on scene.

Incident reporting: near-misses, injuries, and equipment losses are logged and reviewed to update procedures.