Removing Bias in Latitude Estimated from Solar Irradiance Time Series

Abstract

Latitude estimates from light recorded by electronic data storage tags typically contain large errors, particularly at times near the equinoxes. We employ error propagation analysis to the fundamental equation relating latitude to solar elevation and time of day. Large latitude errors are caused by mathematical amplification of small errors in relating solar irradiance to solar elevation. Furthermore, the sign of these errors is such that the estimated latitude is badly biased. This analysis leads directly to a method of removing systematic error (bias) from latitude estimates in state-space track reconstruction models. Preliminary implementation of this method effectively removes all bias from latitude estimated from solar irradiance recorded by archival tags deployed both on moorings and on freely swimming tuna