.. UHDAS+CODAS documentation master file, created by sphinx-quickstart on Wed Jan  7 14:24:39 2009.
   You can adapt this file completely to your liking, but it should at least
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Previous Ping Interference
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


The bottom-bounce from one ping can cause bias in the next ping by making
the bottom reflection appear 'hovering' midwater, like a scattering layer.
The reflection is not strong enough for the single-ping editing algorithm
to identify it as 'the bottom', but the velocities are biased in the same way
as a scattering layer **"S"**, i.e. a lobe of bias in the direction of travel
which shallower than the scattering layer, and a lobe of bias in the opposite direction
deeper than the scattering layer.

In this case, the ship is travelling southwest.


.. image:: 2017-229-1440os38nb_contN.png
   :alt: previous ping interference example
   :scale: 50


--------------

The bottom slopes form 2000m down to 3500.  The problematic depth range at this
3-second ping rate is 2000m-3500m.

.. image:: amp_dday228.png
   :alt: previous ping interference example
   :scale: 50


--------------

This is a diagram showing depth and time, with the previous ping reflecting off the
bottom and being seen (heard) in the subsequent ping.

.. image:: prev-ping.png
   :alt: previous ping interference example
   :scale: 50


--------------

Here is another example:

.. image:: prev-ping-topofig.png
   :alt: velocity vectors over topography
   :scale: 70



.. image:: prev-ping-panels.png
   :alt: velocity (u,v), percent good, signal return, ship speed
   :scale: 70

--------------

You can look up the depth at which a given ping rate will cause previous ping
interference in the figure below:



.. image:: previous-ping-graph.png
   :alt: figure showing the depth at which a given ping rate will have previous ping interference
   :scale: 30



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   :maxdepth: 1