Variability of bio-optical properties at sampling stations and implications for remote sensing: a case study in the north-east Gulf of Mexico

Abstract

Variations of bio-optical properties at oceanographic sampling stations, although important for satellite data validation and algorithm development, have rarely been documented or studied. Using flow-through data and water samples collected from the flow-through system and Niskin bottles at ∼260 stations between summer 1998 and spring 1999 in the north-east Gulf of Mexico (27.5° to 30.4° N, 90° to 80° W), we study the variability of several properties, including chlorophyll-a concentration and Gelbstoff absorption, at the sampling stations. It is found that the standard deviations for both Gelbstoff and chlorophyll are less than 10% of the mean values for more than 90% of the stations, including the coastal stations where water is turbid or Case II. High variations are found in the frontal regions near river plumes. At several stations chlorophyll-a and Gelbstoff vary by nearly two-fold due to spatial and/or temporal variations of the properties near the plume waters. This suggests that for water samples collected from moderately coloured waters (chlorophyll-a >0.25 mg m−3) or coastal river plume waters, special care should be taken to validate the sample data by using multiple samples, a continuous flow-through system, or a concurrent satellite data product map. Otherwise large uncertainties are likely to occur when these data are used to validate satellite estimates.