Two part (question) Poll:
Do you have (and USE) a quality barometer and thermometer for computing your environmental correction in your EDMI?
If so, how often (times a day), if not...why not?
Loyal
Yes
As needed, usually 2-3 times during a typical day.
Having said that, I rarely use the TS other than for distances under a 1000' in the last decade or two.
SHG
Daily (when that equipment is in use).
No, we don't use ASTM standards or equipment for outside air temperature, barometric pressure or relative humidity for that matter. We check the closest NWS recording station to the job site and adjust accordingly.
Like Shelby, most of our TS work is short distance (within established control).
BTW - We peg our levels monthly, even though they may not get used.
I heard of an old surveyor that would fiddle with the ppm on the gun until he got the distance he calc'd on corner to corner shots. That satisfied him that the ppm's were correct for further work - no pesky barometer or thermometer necessary. o.O
I bought a Casio watch about a year ago that has both T&P readouts with the pressure being absolute, instead of seal level corrected which is what you need, seems to check out real solid, certainly good enough to use for the typical short EDMI shots I take these days. I also carry an old school glass thermometer in the instrument case.
The watch is solar powered and also sets itself every night from WWV, very handy having all this on the wrist! A few other useful tools too such as sunrise and sunset, etc.
SHG
> Two part (question) Poll:
>
> Do you have (and USE) a quality barometer and thermometer for computing your environmental correction in your EDMI?
>
> If so, how often (times a day), if not...why not?
>
> Loyal
Always depended on the survey.
Years ago, before built in ppm, recorded temperature and used temp/elevation chart to determine ppm correction to set. Always had thermometer with me and elevations seldom changed more than 300 feet on any given job. Always measured lines from both ends. Learned in those days short lines, less than 500 feet, are less likely to show change with temperature. Lot surveys & in town work would set temp in AM and check at about 2 hr intervals. More often in spring and fall or if weather was changing. Rural surveys with long traverse lines requiring travel time temp was checked beginning of each instrument setup.
With the newer EDMI & total stations started carrying both thermometer and barometer. Still followed the pattern of check more often when observing long lines and in changing weather. Input the temp and pressure and let the instrument compute ppm.
For EDMI baseline checks turn all atmospheric corrections, documented in manufacturers manual, off and observe all stations from 0 point. Turn atmospheric corrections on and observe same stations. Later in office use equations documented in manufacturers manual to compute corrections and compare results. Occupy all stations (usually 4 stations at 0 m 150 m 430 m & 1050 m) and measure to all other stations.
Then use NGS publications and software from Calibration Baseline web page specifically Technical Memorandum NOS NGS-10(pdf) as guide, data on the NGS baseline used and related DOS programs to process all resulting observations.
Please note the manual dates from 1977-1980 era before EDMI commonly had atmospheric input capability. Also have fun attempting to run the programs if you have not used a PC-DOS computer in a while.
I came up through the ranks using a thermometer, barometer and a parasol. I get nervous when I don't check.
Ralph
> The watch is solar powered and also sets itself every night from WWV, very handy having all this on the wrist! A few other useful tools too such as sunrise and sunset, etc.
Without some sort of location information (GPS, cellphone triangulation) how does the watch determine the local time of sunrise and sunset?
I adjust temperature by "feel"... +/- 10°F, knowing the highs and lows for the day. We never adjust barometric pressure. We seldom have shots in excess of 600' here and almost never exceed 1000'.
I know that's heresy, but I figure you're looking for honest responses.
[sarcasm]I just use the local weather report![/sarcasm]
I use the nearest weather station pressure report and my Tundra's built-in thermometer when I'm working in my home area (Sacramento Valley). On the rare occasions that I venture into steeper country, I have a digital barometer/thermometer that I use.
Yes, daily.
I've settled upon using a Kestrel weather meter (I think I have the 3500 model). It measures temperature, pressure, and humidity - accurately, quickly, and in a small package. If you remove the lanyard and holster, it'll likely fit inside your total station case, making it really handy and easy to do EDM corrections.
Am I correct to remember that pressure is most significant, temperature is of medium significance, and humidity is least significant, of the three?
Same here, change temp but rarely pressure. Average shot 100 feet, rarely over 330 feet and I don't think I have ever used the EDM past 660 feet.
S6 has a built in barometer... you stil have to access it though. Temp comes off the truck thermometer.
Check the manual for the instrument. My old Topcon manual gives charts and equations for Temperature and Pressure. The precise adjustment may depend on the optical wavelength the EDM uses.
These charts show about 1 ppm for 2 degrees F increase and -1 ppm for 0.1 inch pressure increase. These are rough values and not constant over the whole operating range. One ppm is 0.001 in 1000, so this shows the settings are not critical for short distances.
However, if you start early on a cool morning and work through the heat of the day, your longer lines would benefit from updating the setting. Certainly you should at least make a good guess each day. Someone who never updates their settings could see 0.05 to 0.10 per 1000 difference between winter and summer extremes.
Unless a big weather front moves in, pressure isn't going to change much. Temperature is more important to keep updated as the day progresses. Humidity has such minor effect on infrared EDM (it was a major effect on microwave measurements) it is ignored for routine work and is not included in this manual. I think NGS baseline calibration does consider humidity.
> I bought a Casio watch about a year ago that has both T&P readouts with the pressure being absolute, instead of seal level corrected which is what you need, seems to check out real solid, certainly good enough to use for the typical short EDMI shots I take these days. I also carry an old school glass thermometer in the instrument case.
>
> The watch is solar powered and also sets itself every night from WWV, very handy having all this on the wrist! A few other useful tools too such as sunrise and sunset, etc.
>
> SHG
I think you meant that the other way. Absolute pressure is what you need, not the relative (sea level corrected)(TV weatherman's) pressure.
I agree, if there was a big swing in temperature during a day's work, it might be significant enough to make an adjustment. In the hill towns where I work, barometric pressure at various sites changes significantly. Difference in elevation from one site to another might be 1000 feet....For those working on the shore, I suppose this wouldn't matter too much.