Mask Angle (static observations) and OPUS

I've always used 13 degrees.

I was taught that below that, the signal is "coming in" through the atmosphere at an angle and that adds distortion. Like the distorted colors of the sun at sunset and sunrise.

:pizza:

edit: I've also increased the mask angle (one degree at a time) when tweaking a post processing session. With great results.

I have always processed (at least the first time through the data) at 15 degrees, but I liked having the option to "go lower" if I wanted to.

I agree about the problems with VERY LOW mask angles, and was a little surprised to see that OPUS has (apparently) dropped to 10 degrees.

Novatel (for example) has a new "3-dimensional" Choke Ring Antenna that is supposed to be very good with LOW (even negative) mask angles, but I don't know if any post processing software has adequately solved the tropospheric problems as yet.

I know that OPUS (well PAGES) has been undergoing continuous refining and upgrading over the years, so maybe they (they NGS) has solved the tropospheric delay issues (at least down to 10 degrees).

Loyal

Thanks for the tip, I probably should tryout a drop down to 10 for my OPUS sessions.

They must have their reasons.

Living in a forested landscape I go from 15-18 degrees depending on what I need to get a solution.

Antenna phase pattern Models

Sometime this year (April/May maybe), the NGS will adopt ITRF2008 (IGS08/NGS2008 whatever), and that will involve a change in antenna phase pattern models (relative to absolute). Therefore, all of us who do own post processing, will HAVE TO adopt the new antenna models IF we want to play by the rules, and have any hope of duplicating the NGS/IGS/SOPAC/PBO etc. results.

In point of fact, we really should have been using them when using IGS orbits since IGS05 became the orbit frame back in November 2006.

NAD83(CORS96a) will of course be intrinsically tied to ITRF-2008, so this means that WE have to stay current with this antenna model change.

The latest (I think) IGS Absolute Antenna Calibration data can be found here:

ftp://ftp.ngs.noaa.gov/pub/pnt6/igs05_1604.atx

How one gets this new data into your commercial post processing software will probably vary somewhat by vendor, BUT I would HOPE that they (the vendors) have this under control.

Keeping up with all of the changes going on with GPS/GNSS is nearly a full time job these days (at least for this old geezer), but that's part of our job if we utilize this technology.

Loyal

The mask angle is set to 8 degrees on the base and 15 degrees on the rovers. Allows me to decrease the mask angle on the rover and 8 degrees for post-processing. Usually I won't use 8 degrees to post-process but I have the option.

Loyal: I have always used 12 (well, at least in the last decade or so). Collecting lower can't hurt, as you can always set a higher value in the software.

In the very early days of GPS we used to process at 18°, probably because the software was not modeling the errors in the low elevation angle data correctly. We collected at 15 then.

I know there a lot of people still using older processing packages, many of which are no longer supported. So, in order to use the absolute models they may need to pay some $$ to upgrade.

> I know there a lot of people still using older processing packages, many of which are no longer supported. So, in order to use the absolute models they may need to pay some $$ to upgrade.

It is things like this that push surveyors over the edge and into retirement.

Maybe NGS software is the answer for us surveyors with PP software that is no longer supported?

I agree John (bout the old software).

I have at least one package that will NOT be "upgradable" to the absolute models.

With all of the research and development going on in GPS/GNSS technology, a guy just HAS TO keep at least one package current and up to date.

It generally ain't free by any means.

Loyal

I set it in the d.c. to cut-off at 13

I'm set at 15° -- Van Sickle suggests 15° to 20° in GPS for Land Surveyors.

I set my mask at 0, always when collection for static. My motive is you can raise the mask in the software but you can't add in stuff that was not collected. Memory is cheap relatively speaking so the extra birds don't actually hurt anything even if you do not use them and raise the mask when processing.

With OPUS, then you often in many areas have some pretty long baselines. A lower mask insures that both units will see the same space vehicles and insures a longer time viewing each space vehicle. Especially true when you are rolling your own with units in the dirt.

I figure more data is good and you can discard what you do not need when evaluating the data sets.

Multipath and the tropo are real concerns but I am of the opinion that more data is better. It allows me to evaluate the significance of each SV on my own instead of using a canned elevation mask.

Zero for me.

I collect at 10° and start processing at 15°. These days I rarely have to futz with the mask.

Well said Deralski...

my feeling exactly!

Ya can't play with that which you don't have (access to)...

🙂
Loyal