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Table 1 Comparison of geolocations based on irradiance, magnetic intensity, and sea surface temperature

From: The value of using measurements of geomagnetic field in addition to irradiance and sea surface temperature to estimate geolocations of tagged aquatic animals

  Irradiance (day length) Magnetic field intensity Sea surface temperature
Sensor cost Low Medium–high Low–medium
Sensor calibration Available from the factory Requires special equipment and magnetically undisturbed site or facility Available from the factory
Field characteristics Naturally smooth, varies with time of year, less of gradient with latitude at equinox than solstice Smooth main field changes slowly over years (intensity, inclination, and declination) with overlaid crustal and man-made anomalies Highly dynamic over time. High gradients in mid-latitudes, low gradients near equator and high latitudes.
Main disturbance Tag fouling, water clarity, diving depth, sea state, tag orientation if directional; cosine correction or wrap-around collector avoids directionality Crustal anomalies associated with magnetic lineations and volcanic seamounts and islands, man-made anomalies of wrecks, rare solar storms Diurnal variations and vertical stratification. Errors arising from small, hot or cold regions or uncertain depth profiles not captured by the model but influencing the tag measurement
Availability at depth Within the euphotic zone, <200 of meters depending on water clarity Present at all depths. Main field uniform at surface, anomalies increase with depth or in proximity to magnetized bodies Mixed layer to a depth captured by model
Typical model error Civil day length computed using astronomical equations. Negligible modeling error Mean error of 152 nT for WMM model. This paper uses site-specific maximum anomaly in 0.25° × 0.25° cells per WDMAM Error of 0.6 °C mean for OSTIA foundation Sea surface (temperature at the indeterminate depth free of diurnal variations)
Typical measurement error ±4 min typical error for measuring equivalent points on the sunrise and sunset irradiance curve. This corresponds to approx. +100/−50% irradiance disturbance due to factors such as weather changes, turbidity changes, animal depth changes and in situ bias compensation A 300-nT residual error after in situ bias compensation 0.1 °C after in situ bias compensation