As optical field equipments have become available, the bio-optical model has appeared and is being widely used, which make it possible to accurately remove the contribution due to water column [22, 23] and then to separate between the signatures coming from water column and bottom.This paper aims to present an approach to estimate the past biomass of aquatic vegetation in a shallow inland lake using the historical satellite imageries without any corresponding field investigations, based on the present satellite imagery provided along with concurrent or quasi-concurrent ground field investigations, and then to determine the historical change of the aquatic vegetation in Taihu Lake.

We first present some general information about Taihu Lake and the field investigation, including instruments and sampling methods, and satellite imageries together with its preprocessing method.

Then we describe the method for developing the quantitative estimation model for aquatic vegetation in Taihu Lake. Finally, some conclusions are drawn on the basis of the full discussion.2.?Study areaTaihu Lake, a large shallow lake with an average depth of 1.9 m (max. 2.6 m), and covering an area of 2427.8 km2 (including 51 islands), is one of the five largest fresh-water lakes of China and is located in the core of the Yangtze Delta in the lower reaches of Yangtze River, in East China, an area that has a developed economy (Figure 1).

Unfortunately, in recent years, water quality has deteriorated and cyanobacteria blooms have covered large areas of the lake every summer since the 1990s.

There exist four types of aquatic vegetation: (a) emerged vegetation, including Phragnites communis, Typha angustifolia, Zizania latifolia and so on, (b) submerged vegetation, including Ceratophyllum demersum, Vallisneria spiralis, P. malaianus and so on, (c) floating vegetation, including Eichhornia crassipes, Lemna minor and so on, and (d) floating-leaved vegetation, including Brefeldin_A Nyphar pumilum, Nymphaea tetragona and so on. They are mainly distributed in the several bays of the east and southeast and in the south littoral zones, where the water is clear and cyanobacteria blooms are rare.Figure 1.Location of Taihu Lake in China.

3.?Material3.1. Field dataThe campaign was carried out along the preset transects Dacomitinib for 94 samples on 10-18 June 2007 (Figure 2), which were positioned by differential GPS (Global Positioning System, Trimble Ltd., USA) with a positioning precision of 2-5 m. Before the field investigations, the sampling locations were preset according to the prior knowledge of the aquatic vegetation distribution with help of a 1:50,000 scale digital topographic map.