Allan, Mathew G.; Hamilton, David P.; Hicks, Brendan; Brabyn, Lars (2015). Empirical and semi-analytical chlorophyll a algorithms for multi-temporal monitoring of New Zealand lakes using Landsat. ENVIRONMENTAL MONITORING AND ASSESSMENT, 187(6), 364.

Abstract
The concentration of chlorophyll a (chl a; as a proxy for phytoplankton biomass) provides an indication of the water quality and ecosystem health of lakes. An automated image processing method for Landsat images was used to derive chl a concentrations in 12 Rotorua lakes of North Island, New Zealand, with widely varying trophic status. Semi-analytical and empiricalmodelswere used to process 137 Landsat 7 Enhanced Thematic Mapper (ETM+) images using records from 1999 to 2013. Atmospheric correction used radiative transfer modelling, with atmospheric conditions prescribed with Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and AIRS data. The best-performing semi-analytical and empirical equations resulted in similar levels of variation explained (r2= 0.68 for both equations) and root-mean-square error (RMSE= 10.69 and 10.43 mu g L-1, respectively) between observed and estimated chl a. However, the symbolic regression algorithm performed better for chl a concentrations < 5 mu g L-1. Our Landsat-based algorithms provide a valuable method for synoptic assessments of chl a across the 12 lakes in this region. They also provide a basis for assessing changes in chl a individual lakes through time. Our methods provide a basis for cost-effective hindcasting of lake trophic status at a regional scale, informing on spatial variability of chl a within and between lakes.

DOI:
10.1007/s10661-015-4585-4

ISSN:
0167-6369