98 / 2023-07-30 13:05:55

A Modified Thermal Lag Correction Method for Glider-Based Salinity Measurements

glider, thermal lag correction, salinity, isopycnic-surface

Autonomous underwater glider (hereafter glider) can offer persistent and fine-resolution observations in the coastal and open oceans, filling crucial gaps left by traditional observing systems (Meyer 2016; Testor et al. 2019). However, errors due to heat stored in the conductivity cells, called "thermal lag errors", cannot be ignored with low frequency sampling glider (Lueck 1990). Which induce salinity spikes and density inversions in the vertical profiles, especially in the strong thermal gradient regions (Liu et al., 2015). Based on Garau et al. (2011), we proposed a modified thermal lag correction method (weight method) for Glider Payload CTD to enhance the consistency of reference profiles in both temporal and spatial domains. When applying weigh method, salinity difference between the downcast and upcast profiles significantly reduced, resulting the reference profiles align each other throughout the water column. Compared to the Garau method, the weight method demonstrates smaller absolute mean salinity difference and higher error reduction rate. Importantly, the weight method avoids introducing salinity spikes at the division points, as observed in the segmented method. Additionally, we introduce a novel perspective for examining thermal lag correction on the isopycnic-surface, which effectively eliminates the mismatch between the downcast and upcast profiles in the vertical direction, particularly in the regions with active internal waves (internal tides). However, even after corrections, certain profiles still exhibit salinity separation in the potential density coordinate, which may be attributed to fronts. In such case, the salinity separation in the corrected profiles is reasonable as the downcast and upcast profiles measure different water masses. Our research improved the accuracy of glider data processing and quality control, and enhance the understanding of oceanographic processes.