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MTL parameter for station in Hong Kong

Started by, August 14, 2019, 09:04:18 AM

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I have been struggling to understand how to use the parameter MTL - NAVD88 and would like to check whether my assumptions are correct :)

I believe that since my topgraphic data (DEM) is not projected into any vertical datum, it would be enough to use a factor that would correct the DEM in terms of MTL, right?

If this is right, I would need to factor of correction which accounts for the Tide Mean Level minus the Local Datum level, right?

The station I am considering as input is the Tsim Bei Tsui (ID=1366), which provides the following diagram:  (diagram attached to the message too).
[attach name=question_mtl.PNG type=image/png]76[/attach]

Is it correct that I should apply the paremeter as" MSL (2001-12) minus Local datum"? In this case, based on the diagram, I would have to use it equals 1.46m.

Can anyone please help me?


Jonathan S. Clough

The DEM must have some vertical datum to which elevations are referenced -- are the elevations in terms of the 1974 datum?

The MTL-NAVD88 parameter is set up such that if you looked at a gauge and there was a referenced MTL height and a referenced NAVD88 height, the value would be the difference of the two numbers referenced.

For example, at this station

MTL is 4.451 and NAVD88 is 3.134 meaning that MTL-NAVD88 would be approximately 1.3 meters.

NAVD88 can be substituted for whatever the datum of the elevation data set is.  So you can convert your datum of elevation to MTL (often ~MSL) and then set the MTL-NAVD88 parameter to zero.

In the case of your figure, if your elevation data are in 1974 datum, MTL-NAVD88 would be 1.46 meters.

Been traveling, sorry about the delay in response -- hope this helps.