
%lesson 7

%\centerline{
%\underbar{ Practical Lessons in Satellite Oceanography}}
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\lessons

\centerline{\bf  OCEANOGRAPHIC INTERPRETATION OF IMAGES }
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\centerline{\bf 7 : AIRBORNE THEMATIC MAPPER DATA - SOUTHAMPTON DOCKS} 
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%\centerline{\bf \underbar{Aim of Lesson}   }
\aims

To provide experience in the analysis and interpretation of
airborne thematic mapper data of an estuary.


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%\centerline{\bf \underbar{Specific Objectives}}   
\objectives

After completing this unit, students should have learned:-

1) to use the image processing toolkit to enhance aircraft scanner
data to clarify coastal topography and to reveal the spatial
patterns of water-leaving radiance

2) to compare ground-control points with a chart of the area in
order to determine the approximate scale and the geometric
distortions in the image.

3) to identify various visible radiance signatures in terms of
surface reflection and water-quality phenomena.


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%\centerline{\bf \underbar{Background Information}}   
\background

{\bf  The Bilko image-processing software }


No prior knowledge of the BILKO system is required.  The online
 HELP  facility, accessed by typing  \type{H}, explains the operation of
the current command and  \key{escape}  returns to the main menu. This
lesson will illustrate the application of some of the facilities
provided by the toolkit, and guidance will be given in using them
to best effect.

 {\bf Other equipment} 

In order to work through this exercise, you will probably find it
helpful to have a calculator, graph paper for plots, and coloured
pencils if you want to sketch some of the features observed.  To
relate the images to the underlying oceanographic processes, it
will be useful to refer to a hydrographic chart covering the
region under study.


 {\bf The images used for this lesson }

Six image datasets are provided for this lesson. They are raw data
from channels one to six of the Daedalus 1268 Airborne scanner,
flown on the Piper Chieftain aircraft of the UK Natural Environment Research Council.  The data were
collected one day

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\centerline{Figure 2.}
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 in September 1987, over Southampton Docks (see Fig. 2).
The six channels of the scanner have the following spectral
characteristics:-

$$\vbox{\offinterlineskip\hrule
\halign{\vrule#&\strut \quad\hfil#\quad\hfil&
\vrule#&\hfil\  #\  \hfil&
\vrule#&\quad\hfil#&#\hfil\quad&#\quad&\vrule#\cr
height10pt&Filename &&Channel  && \multispan3 \hfil\  Wavelength/$\mu$m \  \hfil&\cr
\noalign{\hrule}
height10pt&D11     &&1   && 0.42 &- 0.45 &    &\cr
&D12     &&2   &&0.45 &- 0.52           &*1&\cr
&D13     &&3   &&0.52 &- 0.60           &*2&\cr
&D14     &&4   &&0.605& - 0.625         &  &\cr
&D15     &&5   &&0.63 &- 0.69           & *3&\cr
depth5pt&D16     &&6   &&0.695 &- 0.75  & &\cr
\noalign{\hrule}
\multispan8 \strut\hfil *n = equivalent to band n of the Landsat\hfil\cr
\multispan8 \strut\hfil Thematic Mapper\hfil\cr}
}$$
 Notes on Interpretation of unprocessed ATM data 

Although the data have not been calibrated directly in terms of
radiance, there is a linear relationship between the digital
numbers and the radiance received at the sensor.  Because the zero
offsets and the calibration gradients are different for different
bands, it would be unwise to attempt any quantitative
interpretations based on the raw data, or based on ratios between
different bands of the raw data.  However, band ratios may convey
qualitative information, particularly about whether a feature is
more evident in one band than another.

No geometric correction has been applied.  This means that
distortion is to be expected at scan lime extremities i.e the
across-screen pixel width is variable.  The portion of image
extracted is not the whole width of the scan lines, and is located
towards the centre of the line.  The top-bottom scale is not
necessarily the same as that across the image, but is
approximately uniform throughout the image.  
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%\centerline{\bf  OUTLINE of LESSON }
\outline

The lesson should take at least 30 mins to complete.

1.  Look at each channel in turn and set up an appropriate LUT to
enhance the water patterns in each.  Band 6 should give you the
best means for discriminating the land-sea boundary, and hence
will be most useful in position fixing on the image.

2.  Examine the geometric distortions on the image.  Using a map
of the Docks area try to work out approximate length scales in
both directions.

3.  List the features and patterns present on each image.  Note
which are present on all and which on only some of the channels.
Compare the spectral signature of different features,
qualitatively, by plotting each feature as a line on a graph of
pixel value against channel number.

4. Suggest interpretations of the features observed in 3, and
attempt to distinguish between objects on the water, patterns due
to surface roughness, and patterns due to variation of the optical
properties of the water itself.

5.  Note the large vessel which is moored alongside the dock in
the centre of the image.  It had arrived within a few minutes of
this image being recorded, and the tugboats which have helped it
to berth can be observed leaving it.  Note also the large
plume-like feature to the left of the large vessel.  Suggest what
this may be, by comparing its spectral signature with other more
readily identifiable fatures on the image.

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\byline{I S Robinson,  March 1988.}

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