Altimeter settings (aka QNH) are referenced to mean sea level. It has nothing to do with GPS altitude. If a properly set and calibrated barometric altimeter agrees with a GPS it is just a coincidence, some might say a rare coincidence.
Regards, Garry Lockyer C: +1.250.689.0686 E: [email protected] > On Dec 24, 2020, at 11:06, [email protected] wrote: > > I am nerding out calibrating my barometer today. I have a handheld > precision barometer that I can take co a vertical survey marker close to a > nearby major airport. I can then call the automated message at the tower and > get real time AS (altimeter settings) from the airport barometer. I just am > not sure what height these AS settings are referenced to. There are two > listed in the marker's datasheet. Ortho and Ellipsoid. Ortho is based on > spirit leveling and a better reference to a hypothetical equipotential > surface that is tied to one tide station in Quebec (NAVD88) or the GPS > measured Ellipsoid (a simple oblate sphere that is supposed to approximate > said equipotential surface). The nice thing about doing this is that I can > precisely know the height of my WX station at home. I know it within about 5 > feet, but not certain until I take use an average over time of this AS from > the local airport. I don't have a super expensive Surveyor GPS to determine > it. I do have a surveyors tansit, but I am thinking doing a closed lip with > it from a local vertical control is way overkill even though this stuff is > fun to me :D > > I hope there is someone that is into surveying nerdiness that can answer this > question. If not, I will have to email the local skywarn contact > meteorologist and bug him. > > Regards, > > Chris Maness > > -- > You received this message because you are subscribed to the Google Groups > "weewx-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/50abb7a0-0fc2-fc0c-56ff-3d6e034451af%40gmail.com. > <OpenPGP_0x55BE65AD1B41D696.asc> -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/FDF1A232-6226-426E-B20A-6E55C4EAF7A2%40gmail.com.
