Skip to contents

Double smoothing of positions

double_smoothing.Rd

The raw positions have relatively low precision (Phillips et al. 2004) and also exhibit a typical noon–midnight zigzag pattern in latitude due to east–west movements, and to lesser extent in longitude due to north – south movements (Fox 2010, 2015). To reduce the influence of inaccurate positions and compensate for movements a double smoothing procedure described in Hanssen et al. 2016 can be applied (DOI: 10.1007/s00300-016-1908-z).

Usage

double_smoothing(df, sun)

Arguments

df

data.frame with twilight times as 'tFirst' and 'tSecond' and 'type' (1 = tFirst is morning, 2 = tFirst is evening)

sun

corresponding sun angle for each latitude and longitude

Value

A data frame with six additional columns; 'lat' & 'lon', 'lat_smooth1' & 'lon_smooth1' and 'lat_smooth2' & 'lat_smooth2'.

Details

This function performs the following steps:

  1. First smoothing, essentially compensation for east-west movements (mean lat (lat_smooth1)) and north-south movements (mean lon (lon_smooth1)), noon-midnight.

  2. Compensate for positions crossing the Pacific 180 Meridian

  3. Second smoothing, two point moving average of noon-midnight positions ('lat_smooth2' and 'lon_smooth2'), same as Phillips et al.2004