They're really not needed anymore, with the instruments handling atmospherics automatically.?ÿ Spent a few minutes searching online and haven't found anything.
Does anyone have a hyperlink to one or a pdf of the chart,?ÿ Trying to find the difference between 32?øF and a -15?øF if anyone knows that offhand
We were told to enter temperature and pressure into the data collector daily. I use AccuWeather. Those values don't show up in the raw data. I can't remember the last time I shot a distance over 700 feet. I figure in that short of a distance, PPM won't make a significant difference anyway.
Pressure isn't as big an influence as temperature, and you are at low elevation, but if you are ever involved in a measurement where pressure needs to be considered remember this:
The pressure in most weather reports is adjusted to sea level equivalent, but the correction needs to be from the absolute pressure at your elevation, not sea level.
RJ?ÿ If I read your post correctly you want to know the difference between a EDMI shot at +32 F and one at -15 F at the same distance (?).
If that is correct then you have a total spread of 32+15 = 47 F?ÿ?ÿ The rough rule is for every 1 C (1.8 F) you have 1 ppm.
Therefore?ÿ 47/1.8 = 26.1 ... approx.?ÿ ppm
?ÿ
JOHN NOLTON
PS?ÿ what instruments measure T&P automatically? ?ÿHumidity can be up to approx. 1.6 ppm but more like 1 ppm. That's
why most manufactures set the refractive index to about 0.5 ppm for humidity. Only geodetic EDMI measurements then
worry about humidity.
RJ ?ÿ 2 references for my post above are;
1.?ÿ NOAA Technical Memorandum NOS NGS-10; USE OF CALIBRATION BASE LINES. 1977/ reprinted 1980
(this can be downloaded from the internet).
2. Electronic Distance Measurements/ An Introduction, 4th edition, by Dr. J.M. Rueger (1996).
JOHN NOLTON
PS?ÿ I infer you are talking about Laser or infrared light source and NOT Microwave in your above post.
Be careful with that because of your instrument has the capability to do the correction you may be doing a double correction if you're doing it in your data collector as well.
Make certain your not applying it twice.
PPM starts to matter when your measuring longer distances (100 meters+) or doing something extra precise like control points/industrials etc.
I usually change ppm aprox twice a year. Summer/winter.
Indoors it doesnt really matter as distances are usually short anyway.
Try changing ppm temperature values to -/+ degrees and measure 100-200 meters to get the idea of its effect. Its not that big.
?ÿ
Roughly speaking, for temperature 1 ppm=1?øC (1.8?øF) and for pressure 1 ppm=3 mbar (0.09" Hg). And, 0.1" Hg~100 feet of elevation.
As was mentioned above, weather reporting stations usually (not always) give sea level pressure (SLP) which must be corrected for altitude. I believe they all should give SLP, but if you look at a site like weatherunderground.com that has publishes near real time data from private weather stations, it appears there are quite a few that are station pressure and not SLP. Pressure varies by elevation, but not usually very much by area (unless a front is passing through), meaning a pressure from a weather station can be used (corrected for altitude) over a somewhat large area. Temperature, on the other hand, does vary by area due to numerous factors, and also by altitude, about 0.0065?øC per meter, or about 3.6?ø per 1000 feet. So best to use a local temperature if possible.?ÿ
My first robot was a Zeiss S10, very accurate instrument but also very heavy. It had on board T and P sensors. I currently have an S6 and an SX10, both have onboard pressure sensors but not temperature. I have found the P sensor on the S6 to be very accurate. I usually use my phone to get the temperature, although I do have a Brunton ADC Pro and a Kestrel D3 for accurate work, and still have a couple of mercury glass thermometers but I don't like to use them as they are fragile.?ÿ
I also have a weather station at my office, right beside one of the two pedestals we use for checking/calibrating instruments.?ÿ
?ÿ
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It sends data every few minutes to a server. The server stores it with many other stations, but also provides an analysis of the data versus predicted:
So it is plenty accurate enough to get 1 ppm accuracy in the correction for the baseline, which is about 150 m long.?ÿ
