Structure and influence of tropical river plumes in the Great Barrier Reef: application and performance of an airborne sea surface salinity mapping system

Abstract

Input of freshwater from rivers is a critical consideration in the study and management of coral and seagrass ecosystems in tropical regions. Low salinity water can transport natural and manmade river-borne contaminants into the sea, and can directly stress marine ecosystems that are adapted to higher salinity levels. An efficient method of mapping surface salinity distribution over large ocean areas is required to address such environmental issues. We describe here an investigation of the utility of airborne remote sensing of sea surface salinity using an L-band passive microwave radiometer. The study combined aircraft overflights of the scanning low frequency microwave radiometer (SLFMR) with shipboard and in situ instrument deployments to map surface and subsurface salinity distributions, respectively, in the Great Barrier Reef Lagoon. The goals of the investigation were (a) to assess the performance of the airborne salinity mapper; (b) to use the maps and in situ data to develop an integrated description of the structure and zone of influence of a river plume under prevailing monsoon weather conditions; and (c) to determine the extent to which the sea surface salinity distribution expressed the subsurface structure. The SLFMR was found to have sufficient precision (1 psu) and accuracy ( f 3 psu) to provide a useful description of plumes emanating from estuaries of moderate discharge levels with a salinity range of 16 to 32 psu in the open sea. The aircraft surveys provided a means of rapidly assessing the spatial extent of the surface salinity distribution of the plume, while in situ data revealed subsurface structure detail and provided essential validation data for the SLFMR. The combined approach allowed us to efficiently determine the structure and zone of influence of the plume, and demonstrated the utility of sea surface salinity remote sensing for studying coastal circulation in tropical seas. D

Satellite-based monitoring of tropical seagrass vegetation: current techniques and future developments

“…Yet, remote sensing has a potential to offer more than localizing the distribution of seagrass meadows. Remote sensing may also be used to detect environmental conditions affecting seagrass status, such as the detection of sediment plumes (Burrage et al, 2003;Nezlin et al, 2005). In terrestrial systems remote sensing has been applied to detect concentrations of foliar nitrogen (Lilienthal et al, 2000;Mutanga et al, 2003;Ferwerda et al, 2005;Skidmore et al, 2005) and photosynthesis levels (Zhao et al, 2005) in plants.…”

“…They found that the primary factors regulating the relationship between rainstorms and sediment plumes were watershed land-use characteristics, size, and elevation. Burrage et al (2003) used a prototype Scanning Low Frequency Microwave Radiometer (SLFMR) to describe the structure and extent of a river plume. The SLFMR was found to have sufficient precision (1 psu) and accuracy (3 psu) to provide a useful description of plumes emanating from estuaries of moderate discharge levels.…”

Remote sensing of environmental indicators of potential fish aggregation: An overview

“…Airborne microwave radiometers have been used to determine the structure and influence of river plumes, since the input of freshwater plumes from rivers is a critical consideration in the study and management of coral and seagrass ecosystems (Burrage et al 2003;Burrage et al 2008;Wang, Heron, Hacker 2007). Low salinity water can transport natural and man-made river-borne contaminants into the sea, and can directly stress marine ecosystems that are adapted to higher salinity level.…”

Evaluation of a New Airborne Microwave Remote Sensing Radiometer by Measuring the Salinity Gradients Across the Shelf of the Great Barrier Reef Lagoon

“…In 2000, an instrument that is based on the prototype SLFMR [5], [11], [13] was constructed for an Australian research consortium by Quadrant Engineering (now ProSensing), Amherst, MA. The SLFMR instrument has been used in the study of the estuarine plume of the Herbert River in the Great Barrier Reef (GBR), and results on the structure and influence of tropical river plumes were obtained [3].…”

“…For the Australian SLFMR, the absolute accuracy of the instrument was empirically determined by using in situ observations with a conductivity-temperature-depth (CTD) probe, and it was found that the calibration with respect to groundtruth data drifted over a salinity range of 3 psu [3]. To improve the precision, a new-generation microwave radiometer was developed in 2004 based on the SLFMR and the STARRS radiometer technology.…”