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Oceanography
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The dynamic Remote Sensing monitoring of the east four outlets in Pearl river estuary and its application on offshore engineering
The qualitative and quantitative interpretation of flow field
suspended sediment and topography of shoals
- Interpretation Marks for the flow field at the outlets
The momentary situation of water surface and the sediment in the upper is recorded on remote sensing images The changes in flow fields will cause a change in the spectrum characteristics of the surface layer which can be shown in the images By means of inter lines and the difference among grey gradients flow filed features can be identified such as the main flood tide and ebb tide current the intersection of runoff flow and tidal currents the intersection of the flow out of neighbouring outlets with the dominant flow the mixing of salty water and fresh water etc.
- The Quantitative Interpretation for Suspended in the Estuary
In this study the TM CCT received by China remote Sensing Ground Station (Beijing) are used to search the way for quantitative interpretation of surface suspended sediment concentration The experimental process and methods are as follows.
- Synchronous and Quasi-Synchronous Survey
TM CCT data received on 8 December 1987 were taken for information source while synchronous and quasi-synchronous survey at the east four outlets and in the channel outside the outlets was undertaken in 8 and 24 December The main purposes of observation were flow direction, velocity, depth and suspended sediment concentration The survey time was 9 to 11 am Since the tidal pattern and the flow condition upstream of the outlets on 24 December are closely similar to those on 8 December when the satellite passed over the site the observation on 24 December can be considered as a quasi synchronous one.
- Wave band Selection and correlation Analysis
Datum characteristics of different wave based on TM images are compared and analyzed in this study such as the brightness range bar chart etc it is shown that all the ratio of TM3 TM4 and TM4/TM2 can indicate the difference in suspended sediment concentration Taking the ratio wave bands for the variables in the correlation equation has the advantage that no effect of the changes in illuminance solar elevation and scan angle would occur further more, it can get rid of absolute radiation standardization for the data to be translated there for ratio TM4/TM2 is taken for correlation analysis with survey data of sediment load. Yielding:
Log S = 0.669E + 1.262
Where S is suspended sediment concentration (mg/1) E is the ratio Tm4/TM/2 in order to check the accuracy due to the equation a verification in undertaken using the survey data at 8 survey points on the image of another time phase it is shown that the accuracy can generally meet the need of application.
Table. 1Verification of the Equation
| Ratio TM4/TM2 |
1.094 |
0.834 |
0.902 |
1.812 |
1.405 |
1.210 |
1.528 |
0.412 |
| Calculated S (mg/l) |
98 |
66 |
73 |
298 |
159 |
118 |
192 |
35 |
| Surveyed S ( mg/l) |
140 |
68 |
83 |
304 |
169 |
110 |
156 |
30 |
| Error (%) |
-30 |
-3 |
-12 |
-2 |
-6 |
7 |
23 |
7 |
- Interpretations for Shoal Pattern at the Estuary
Interpretations of TM data in low flow and low tide period for the type and pattern of shoals at outlets and the present situation of offshore reclamation works can be undertaken by means of proper linear contract stretch and categorization of the wave band group TM4, TM5 , and Tm2 with computer In order to compare the present data with historical data about the evolution of shoals the border line between water and land is transitted into isobath for this more survey work was done at more points to get depth and level data when the satellite passing over the site so that the error to water surface gradient could be rectified.
Fig. 1 TM Image of Lingdingyang Bay in low flow
and low tide
(08 / 12 / 1987 )
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