HRP FAQ
 


How many of them are there?

    One.  It makes life exciting to only have one- there are several
    back-up release mechanisms built into the hardware and software
    based on mechanics, chemistry, acoustics and computers, but 
    everytime it gets deployed there is a slight chance that it 
    won'tcome back.
Has it ever hit the bottom?
    Unfortunately, yes it has.  We often attempt to profile to within
    10-15 meters of the bottom.  Since it will drift sideways as it
    falls through the water, there is no way to know exactly where 
    it will encounter the bottom. So we turn the altimeter on well 
    above the expected bottom depth. If the altimeter cannot sense 
    the bottom, and the pressure for release is deeper than the 
    actual bottom, it will crash.  We have gotten it back every 
    time, though, usually with minimal damage to the sensors.
How many profiles has it done?
    Over 880!  The HRP has proven to be a very reliable instrument
    for making these kinds of measurements.
Which end is up?
    When the HRP is deployed, it falls with its long axis vertical.
    The sensors are at the bottom, so they acquire the data before 
    the HRP mixes things up by going through the water.  The 
    lifting bail, strobe light and radio beacon are on the top.  
    The HRP rides on its side while on deck for ease of handling.
Why does the HRP have whiskers?
    The whiskers are on the profiler to create turbulent flow around 
    the top and to make it rotate along its axis as it descends.  By 
    adjusting the angle of the wiseacres you can increase or  
    decrease the fall speed and change the direction and rate of  
    rotation.
Why do you want it to rotate?
    Because we need to have some known instrument movement in order 
    to convert the velocity of the water measured relative to the HRP 
    to actual east and north.  The internal compass and accelerometer 
    pairs on the top and bottom of the instrument measure the
    instrument's movement- during the data processing, a model of
    this movement is used to convert the raw velocity measurements
    to geographic coordinates
How long do you spend at sea?
    Our cruises with the HRP are typically about a month long.  We 
    often work far from shore, and the transit to the site can be
    three days or more, so the cruises tend to be fairly long.





Can you work in rough weather?

Yes we can. Since most of the time the HRP
is in the water, it is way below the surface,
our main concern is that it doesn't get damaged
on deployment or recovery. We think about
shutting down operations when the wind is
above 30 kts and/or the waves are larger than
15 feet. The picture at the left shows scientists
preparing to recover the HRP in rough seas.















ready for a night recovery

Do you work at night?

Yes, we work 24 hours a day. Normally we
take enough people to make either two 12
hour watches or three 8 hour watches.
We try to allocate the timing of the watches
so no group has to work completely in the dark.
It is much more challenging to recover the HRP
at night, because all you can see of it is its strobe
light.



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