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Poster Session
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Remote determination of the sea-surface chlorophyll a concentration along the coastal water by FY-1 satellite
- Retrieving of the Sea-surface Chlorophyll a Concentration
Based on the option properties of chlorophyll a in the seawater, the chlorophyll a has a strong absorbance at blue (443nm) and a maximum reflectance at green (550nm). In the ocean color remote sensing experiment, usually the ratio of blue and green reflectance is developed to estimate the sea-surface chlorophyll a concentration.
From equation (3) and (7), the sea-surface equivalent albedoes of ocean channels can be easily obtained.
Aw(i) = (As (i)) / Ta(i)
= (As(i) - As(2) * Eo(1) / o(2)
* (l1 / l2)B / Ta(i) -----------------------(9)
(I = 3.4)
and the ratio two ocean channel's equivalent albedoes is as follows
R = Aw(3)/Aw(4) = As(3) - As(2) * (Eo(2) / Eo(3)) *
( l3 / l2 )B /
As(4) - As(2) * (Eo(2) / Eo(4)) *
( l4 / l2 )B * Ta(4) / Ta(3)
---------------(10)
Because of the centre wavelength of channels 3 is very close to that of channel,4 we shall assume that ratio of two average atmospheric transmittances equate to 1. Equation (10) could be rewritten as
R = As(3) - As(2) * (Eo(2) / Eo(3)) *
( l3 / l2 )B /
As(3) - As(2) * (Eo(2) / Eo(4)) *
( l4 / l2 )B
---------------(11)
Then, the sea-surface chlorophyll a concentaion can be retrieved form a power function of sea-surface equivalent albedoes. Generally, we used the following formula:
Nc = a * P-b
---------------(12)
In our calculation, a and b are taken 3.3336 and 5.2316 respectively, which are obtained form solving eq. (12) with two known chlorophyll a concentration data only.
Distribution of sea-surface chlorophyll a concentration at Bohai Bay
Fig. 2 is a four visible channel rude image which was obtaind form FY-1 satellite at its orbit on Sept. 21, 1988. the distribution of sea surface chlorophyll a concentration retrieved by above method is showed in Figure. 3 The grey shades of the image will correspond to definite levels of chlorophyll a concentration as indicated by the grey wedge shown on top of Fig. 3. It is obvious that the concentration is lower than 0.6 mg/M3 between the peninsulas of Liao Dong and Shan Dong, as well as at middle of the Bohai Bay. Generally, it is about 2.5 mg/m along the coastal zone. There is a higher concentration patch at the Laizhou bay. Near the river estuary, such as Yellow River, Haihe and Liaohe River's, the concentration is the highest, usually, over 5.0 mg/m3. That is because those rivers discharge a large of nutrient materials into the Bohai Bay, and make the phytoplankton rich and blooming.
Fig. 2 FY-1's rude images of four visible channels
Fig. 3 The distribution of sea surface chlorophyll a concentration at Bohai Bay
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