Atmospheric corrections

My TS06 Plus has an auto setting so I presume, from the manual, that it uses the temperature and pressure it measures.

On layout projects, my robot get it measured an input every two hours. I get the data from the nearest weather station via my phone. Years ago, we had barometers and themometers in the 2B gun box.

When I was about 13, we did a test where we ran the pressure up and down and the temp up and down and saw the differences. From then till 2008, we set it by an average pressure and temperature about once a quarter. All layout was done with a chain till then and temp corrected with tensioners. Amazingly, having gone back on old control ran in this way with GPS, was not a bad idea.

To be fair, we don't work in an area with a ton of vertical relief like the mountains where the pressure would be all over the map like [USER=228]@Loyal[/USER] does. If I did, I would probably adopt his method.

I have a thermometer in the instrument case, beware that the pressure you need to enter is the station pressure (NOT corrected to sea level). At my office that is around 27 in HG, so NO you DO NOT want to get pressure from the news unless you are located at sea level. If you do, you will need to correct it for you elevation at your project. My total station also has provision to input elevation rather than pressure, BUT that is only going to be approximate because weather systems aren't obviously going to be accounted for.

I have a fancy watch these days with both pressure and temperature and it is pretty accurate (when off my wrist).

SHG

All Total Stations that I used (before retirement) did not have the ability to monitor T&P.

We always took Temperature at instrument height and had barometers. For Humidity (geodetic work) we had a sling psychrometer.

I have the following that I use for all my toys. 2 American Paulin Barometers that I set with my mercurial barometer. I also
have 1 electronic barometer. I have a battery operated Psychrometer (wet and dry bulb readings for Humidity correction).

I use the manufacture equations for correction to their reference refractive index.

Need Lasers in my LDM-2 Terrameter and my Model 8 Geodimeter; hope to get that done this year

JOHN NOLTON.

Shelby H. Griggs PLS, post: 416594, member: 335 wrote: ....beware that the pressure you need to enter is the station pressure (NOT corrected to sea level)....., so NO you DO NOT want to get pressure from the news ...

Do not get pressure from the weather report. That is corrected to sea level.

I have a Brunton Nomad for the pressure. There is a thermometer on my truck for temperature. There is also a thermometer on the Nomad but it takes a solid hour to stabilize.

There is an app that has station pressure

Like Shelby, I use my watch. I usually read it when I'm not wearing it, otherwise it'll pick up my body heat.

Kestrel?

Getting a barometer reading / altimeter setting from airports IS a good idea: they are accurate. Knowing what to do with an altimeter setting is called: knowing what you're doing. Converting sea level pressure, accurate to your proximity, to station pressure isn't hard, mostly a graph, or even a low order calculator routine.

My Casio has twin sensors for barometer. Temperature is okay if making an allowance for body temperature (easily calibrated). Here the temp changes as much as 40 degrees throughout the day. So I usually average it to what is forecast.

I like that idea of getting barometer from the local airport. Never thought about that - thanks. Doesn't NOAA have a local barometric web site?

The above post by Larry Scott is correct but one thing must be added.
You cannot be that far from the weather station to convert back from sea level to station pressure.
The calculations are easy now (2017) because you can find many internet sites that will do the calculations for you.
Its a simple calculation to go from one to the other (sort of).
Before hand held calculators (HP, 1972) you used Logarithms and the Smithsonian Meteorological Table (I still have both).
Go to drkfs.net/correctiontosealevel.htm for some good information.

JOHN NOLTON

Note: you can use a very easy conversion from sea level pressure to station pressure, if you know your elevation (you can
get it from a topo map) for each 30 meters difference in elevation there is 0.1 inch of Hg difference. Minus if station is above sea level.
So if you are at +300 meters elevation then 300m/30m = 10 and 10 times 0.1 = 1 inch; or 1 inch of Hg less that the reported sea level pressure.
Good enough for all but geodetic work.

Here is what I use to convert SLP to station pressure:

pressfact = ((288 - 0.0065 * H) / 288) ^ 5.2561 (H in meters ABOVE SEA LEVEL, not the ellipsoid)

https://www.pce-instruments.com/us/measuring-instruments/test-meters/barometer-pce-instruments-barometer-pce-thb-38-det_2131307.htm

In John Hamilton post above the equation on the right side is OK but what is pressfact?? (what do you mean John Hamilton)

This equation is found on page 268 of the Smithsonian Meteorological Tables, 6th revised edition, 1951

The equation as in the book: p sub z/p sub 0 = ((288-0.0065 z)/288)^5.256
p sub z is the pressure at an altitude above mean sea level in meters
p sub 0 is the standard sea level pressure ( 1013.25 mb or 29.921 inches Hg )

Multiply each side of the equation by p sub 0 and we get

p sub z = p sub 0 ((288-0.0065 z)/288)^5.256

numerical example: we will infer a standard atmosphere.

sea level pressure 29.92 in Hg and z will be 1000 meters (the altitude of your station that you are trying to find the pressure at)

therefore p sub z = 29.92 ((288-0.0065 X 1000)/288)^5.256 = 26.537 round to 26.54 inches of Hg of pressure at your station.

Note: in Hamilton equation he has to the power of 5.2561 but the book has 5.256. Also for sea level pressure I use 29.92 and not 29.921
NO BIG DEAL.

No lets look at the rough equation I gave above with the same numbers I use in this post.
1000m/30m = 33.333 and 33.333 X 0.1 = 3.33 in Hg since we are above sea level we will subtract 3.33 from 29.92 = 26.59

The difference is 26.59 - 26.54 = 0.05 inches of Hg This is 1/2 ppm

In the State of Pennsylvania the highest point is Mount Davis at 3213 feet (979 meters)

JOHN NOLTON

I took that right out of the software I wrote, so pressfact is a factor that is multiplied by the SLP to get SP (station pressure). Because, in my software there is the option to be either SLP or SP, in the case of SP then pressfact is 1.

In my above post I had to sign off because I was having a shipping container delivered. I will finish up what I would have put in the above post.
On page 273 of the Smithsonian Meteorological Tables there is a Standard Atmosphere Altitude-Pressure Table.
If we enter the table with an altitude (your station elevation above or below sea level we can get the pressure. The table is in FEET.
If we use an elevation of 1000m = 3280.8 feet (approx.) we will see that we will have a station pressure of 26.54 (linear interpolation required).
This is the same as the formula ( of course) .
The method used is up to the user but for the flat land surveyor an easy interpolation is down and dirty and gives nearly the same results.
You can go up to 10,000 feet and still only be approximately 1ppm off by using the rule of -0.1 inch of Hg for every +100 foot change of elevation.

JOHN NOLTON

PS If you want to be exact call the weather station and ask them what equation they use to reduce to sea level then just solve for station pressure by changing the equation. And the easiest is once you get the equation is use the internet and fill in the blanks.

A calibrated Barometer at each end of the line.

JOHN NOLTON

Not to get between John and John, but here's what a surveyor/geologist (not geodesist) uses for conversions. This is the main page from the NWS - El Paso "Weather Calculator".

http://www.weather.gov/epz/wxcalc

Page for station pressure.

http://www.weather.gov/epz/wxcalc_stationpressure

And here is a PDF containing the formula used to compute station pressure.

http://www.weather.gov/media/epz/wxcalc/stationPressure.pdf

I see that the formula uses the value of 5.2561 for the exponent.

Since most of my work is in mountainous terrain, the only time I use station pressure (DIA) is as a check of my weather instruments when I use the Arsenal CBL. I have two Brunton ADC Pro weather instruments, an alcohol thermometer and a Thommen barometer. I attach the ADC Pros to the FS and BS tripods using the bayonet mount for the Wild tripod plumb bobs. My wife sewed a couple of "skirts" to place at the top of the tripods so that the ADC Pros are shaded.

The Brunton ADC Pro weather instrument has a function that stores the temperature, pressure, and relative humidity. They can be programmed to collect the data every few minutes (I collect every 10 minutes). At the end of the day I download the weather info using Brunton's IR tool. I set the EDM to 0 ppm and make the atmospheric corrections in the office.

Gene Kooper, post: 417884, member: 9850 wrote: Not to get between John and John, but here's what a surveyor/geologist (not geodesist) uses for conversions. This is the main page from the NWS - El Paso "Weather Calculator".

http://www.weather.gov/epz/wxcalc

Page for station pressure.

http://www.weather.gov/epz/wxcalc_stationpressure

And here is a PDF containing the formula used to compute station pressure.

http://www.weather.gov/media/epz/wxcalc/stationPressure.pdf

I see that the formula uses the value of 5.2561 for the exponent.

Since most of my work is in mountainous terrain, the only time I use station pressure (DIA) is as a check of my weather instruments when I use the Arsenal CBL. I have two Brunton ADC Pro weather instruments, an alcohol thermometer and a Thommen barometer. I attach the ADC Pros to the FS and BS tripods using the bayonet mount for the Wild tripod plumb bobs. My wife sewed a couple of "skirts" to place at the top of the tripods so that the ADC Pros are shaded.

The Brunton ADC Pro weather instrument has a function that stores the temperature, pressure, and relative humidity. They can be programmed to collect the data every few minutes (I collect every 10 minutes). At the end of the day I download the weather info using Brunton's IR tool. I set the EDM to 0 ppm and make the atmospheric corrections in the office.

Gene: I use the same device. The IR connection is a bit flaky, alwyas takes a few tries to connect.

I believe I got the formulas from the el paso page, I have it bookmarked.

John Hamilton, post: 417886, member: 640 wrote: Gene: I use the same device. The IR connection is a bit flaky, alwyas takes a few tries to connect.

I believe I got the formulas from the el paso page, I have it bookmarked.

By the way iPhone 6 has its own barometric sensor. There are plenty of apps that'll display station pressure from the phone's sensor. (Beware that there are apps that simply query the internet.)

This one (link below) displays SLP or Sta pressure based on phone sensor. I've checked this against my aircraft altimeter, desktop barometer, paulin altimeter, and nearby (3 mi away) airport. It's pretty darn consistent. A few 1/100s inch.

Simple Barometer by Friends of The Web, LLC

https://appsto.re/us/PB_92.i

I love my Paulin but it doesn't have s mercury scale. So I have a couple of HP41 routines based on the ICAO standard atmosphere.