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    Re: Suitable Sites for Dip Measurements?
    From: Bruce J. Pennino
    Date: 2013 Apr 2, 19:57 -0400
    Hi John:
    Pru tower is a good idea.  Do you have a value of the deck above MSL? Any problems with getting tripod and equipment to deck. I just checked and the deck is on the 50 tieth floor? Elevation 500 ft or so?

    ----- Original Message -----
    From: John H
    Sent: Tuesday, April 02, 2013 6:54 PM
    Subject: [NavList] Re: Suitable Sites for Dip Measurements?

    The observation deck at the Prudential Tower is a good spot - you can get quite high up and also get a view of the horizon.  Unfortunately you have to pay, but it works.   I've had a number of students go there to experiment with dip angle measurements.    

    If you do try to work with dip angle measurements, be sure to get some measurements on nearby locations (e.g. Fenway Park) - it's interesting to track the refractive effects and how they scale with distance, dip and altitude.  

    I hadn't thought of Blue Hill, but that sounds like a place to try as well.   Again, I'd suggest taking measurements of objects below the horizon dip that you can ID so that you can track refractive effects. 

    Please report back, I'm curious to see what you find out.  

    On Tue, Apr 2, 2013 at 6:27 PM, Bruce J. Pennino <bpennino.ce---net> wrote:


    I'm looking for a convenient site(s) where I can measure dip angles with heights of eye between 150 to 550 ft. I already have in mind several spots on Cape Cod where I can measure from 10 ft to about 150 ft or so. I'm willing to drive two or so hours from Worcester, Massachusetts. From where I live, the Boston south shore is quite convenient, Rhode Island is good, and around Mystic or thereabouts works.

    Ideally there would be some vertical datum control point or NGS vertical bench mark close by. For a very good site I would establish via surveying a temporary bench mark from the known datum.

    The datum control must exist.....still be there today. Many NGS control points are gone, especially on Cape Cod. Many points have been seriously disturbed and unfortunately "put back". If you think you know a good site, please check NGS data sheets. Many Geodetic survey point are now overgrown or so surrounded by trees that they are worthless for this purpose. State DOT bench marks can be just as good, but these are mostly located along state roads. Some towns have excellent GIS system with control points. These control points could also work. If you are a Professional Land Surveyor with the most up to date equipment, we could easily establish a convenient viewing point.Or,if you happen to have a GPS that we can confirm its accuracy, that might work.

    I'd like to do several "heights" on one day so the dip data would be recorded under more or less constant meteorological conditions.

    Another option is a site with an easily traversed hill. I would establish a TBM on the top of the hill based on water level via trigonometric leveling. Then go in 50 ft vertical increments to get dip data. With my EDM and prism , I can "shoot" 1000 ft, but I've never gone this far. I've done 500 ft shots many times.

    If you think you know a good site, please phone me home --- I'd prefer that we don't clutter NavList with these "local" conversations. But OK to clutter if convenient and interesting: My home address is: 35 Woodridge Road, Holden, MA 01520

    Thank you,

    Bruce J. Pennino, P.E.
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