Look up the marine light attenuation model for a location and date

Finds the marine area (ecoregion and clear/turbid water type) that contains the location, and the seasonal model for that area, from the Environment and Climate Change Canada (ECCC, 2026) models of Kd as a function of wavelength.

Usage

marine_kd_model(lat, lon, date, Kd_wvl = 375)

Arguments

lat: latitude, decimal degrees.
lon: longitude, decimal degrees.
date: date, as a Date object or a character in a standard format (e.g., "YYYY-MM-DD"). lat, lon, and date are recycled to a common length.
Kd_wvl: reference wavelength in nm at which Kd_ref is calculated. Default 375.

Value

A data frame with one row per location and columns area, ecoregion, water_type, season, Kd_ref, Kd_wvl, Sk, slope, intercept, r2, the quality flags nodata, peak, vpf_area, and vpf_time, and dist_km (the distance to the area; 0 if inside it). Kd_ref and Sk are NA when the model has no data (nodata is TRUE), which occurs in some Arctic areas in winter.

Details

The ECCC models describe the diffuse attenuation coefficient as log10(Kd(wavelength)) = intercept + slope * wavelength. They were fitted to satellite observations at visible wavelengths (up to 490 or 555 nm, depending on the area and season) and are extrapolated to shorter wavelengths (down to 280 nm). They are converted to the form used by the TUV model, Kd(wavelength) = Kd_ref * exp(Sk * (Kd_wvl - wavelength)), with Sk = -slope * log(10) and Kd_ref = 10^(intercept + slope * Kd_wvl). This is exact for any Kd_wvl.

Seasons are meteorological: winter (December to February), spring (March to May), summer (June to August), and fall (September to November).

If a location is not within any area, the nearest area within 25 km is used, with a message. Otherwise an error is raised.

Examples

marine_kd_model(lat = 49.15085, lon = -125.91427, date = "2024-06-21")
#>                    area      ecoregion water_type season   Kd_ref Kd_wvl
#> 1 Southern_Shelf_Turbid Southern Shelf     turbid summer 0.846611    375
#>            Sk        slope intercept        r2 nodata  peak vpf_area vpf_time
#> 1 0.008755957 -0.003802664  1.353683 0.9808947  FALSE FALSE    FALSE    FALSE
#>   dist_km
#> 1       0