CORS Users Warning
Posted: Mon Oct 26, 2015 10:37 pm
Several CORS in the state of California currently have known errors in height (primarily) at this time. This information came to me via the Oregon State NGS advisor, BUT I am sure is known by at least a few users in California too as the red flag was raised by a Senior Transportation Surveyor at CALTRANS. His summary is as follows:
The stations with the substantial differences in the height component are located in the either the San Joaquin or Sacramento Valley. Some regions in these valleys are continually moving downward, primarily because of ground water pumping induced subsidence. However, due to the 4 year plus drought California is experiencing, we are now seeing subsidence rates in the 1’ per year, or greater, magnitude. The two stations near Bakersfield have move downward at a consistent rate, so if one was using them for control, they would “fit” together, but the resulting heights for any points established from these control would be 14-15 cm lower than what you thought they were.
I just thought you all might find this interesting, if not alarming. Hopefully a full list of out-of-tolerance stations will be published in a future edition of the weekly CORS newsletter and/or on the NGS website to alert users to this situation.
The table formating did not come through very well in the table below, BUT hopefully will be usable.
NGS CORS Positional changes – IGS08 (Current – 2010.00)
10/1/15
BKR1 CA Diff Avg. N [cm] = -0.66 ± 0.22 E [cm] = -2.15 ± 0.25 U [cm] = -14.52 ± 0.92 Bakersfield
BKR2 CA Diff Avg. N [cm] = -0.76 ± 0.24 E [cm] = -1.33 ± 0.29 U [cm] = -14.72 ± 0.94 Bakersfield
MONP CA Diff Avg. N [cm] = 0.56 ± 0.18 E [cm] = -3.96 ± 0.32 U [cm] = -1.19 ± 0.62
ORES CA Diff Avg. N [cm] = 1.18 ± 0.14 E [cm] = -0.26 ± 0.17 U [cm] = -8.67 ± 0.52 Los Alamos
P056 CA Diff Avg. N [cm] = -0.17 ± 0.15 E [cm] = -1.48 ± 0.20 U [cm] = -21.45 ± 1.55 Porterville
P066 CA Diff Avg. N [cm] = -1.15 ± 0.16 E [cm] = 3.20 ± 0.25 U [cm] = -0.33 ± 0.66
P259 CA Diff Avg. N [cm] = 0.19 ± 0.12 E [cm] = 0.50 ± 0.16 U [cm] = -4.66 ± 0.63
P271 CA Diff Avg. N [cm] = 0.02 ± 0.17 E [cm] = 0.20 ± 0.18 U [cm] = -10.67 ± 0.73 Woodland
P300 CA Diff Avg. N [cm] = 2.08 ± 0.12 E [cm] = 3.67 ± 0.15 U [cm] = 1.17 ± 0.29
P304 CA Diff Avg. N [cm] = 0.93 ± 0.13 E [cm] = 3.60 ± 0.15 U [cm] = -6.76 ± 0.45 Mendota
P307 CA Diff Avg. N [cm] = 0.73 ± 0.20 E [cm] = -1.23 ± 0.27 U [cm] = -13.10 ± 0.93 Madera
P565 CA Diff Avg. N [cm] = -0.77 ± 0.16 E [cm] = -1.06 ± 0.17 U [cm] = -23.45 ± 1.36 Delano
P671 CA Diff Avg. N [cm] = 1.24 ± 0.33 E [cm] = -2.02 ± 0.18 U [cm] = -0.38 ± 0.95
PLSB CA Diff Avg. N [cm] = -2.38 ± 0.13 E [cm] = 0.17 ± 0.13 U [cm] = -19.85 ± 0.38 Woodland
SNI1 CA Diff Avg. N [cm] = 0.61 ± 0.26 E [cm] = -2.05 ± 0.38 U [cm] = 1.37 ± 0.98
Hope this helps to avoid some head scratching from anyone using these CORS. I suspect there nay be others too.
Shelby H. Griggs
CA PLS 6785
The stations with the substantial differences in the height component are located in the either the San Joaquin or Sacramento Valley. Some regions in these valleys are continually moving downward, primarily because of ground water pumping induced subsidence. However, due to the 4 year plus drought California is experiencing, we are now seeing subsidence rates in the 1’ per year, or greater, magnitude. The two stations near Bakersfield have move downward at a consistent rate, so if one was using them for control, they would “fit” together, but the resulting heights for any points established from these control would be 14-15 cm lower than what you thought they were.
I just thought you all might find this interesting, if not alarming. Hopefully a full list of out-of-tolerance stations will be published in a future edition of the weekly CORS newsletter and/or on the NGS website to alert users to this situation.
The table formating did not come through very well in the table below, BUT hopefully will be usable.
NGS CORS Positional changes – IGS08 (Current – 2010.00)
10/1/15
BKR1 CA Diff Avg. N [cm] = -0.66 ± 0.22 E [cm] = -2.15 ± 0.25 U [cm] = -14.52 ± 0.92 Bakersfield
BKR2 CA Diff Avg. N [cm] = -0.76 ± 0.24 E [cm] = -1.33 ± 0.29 U [cm] = -14.72 ± 0.94 Bakersfield
MONP CA Diff Avg. N [cm] = 0.56 ± 0.18 E [cm] = -3.96 ± 0.32 U [cm] = -1.19 ± 0.62
ORES CA Diff Avg. N [cm] = 1.18 ± 0.14 E [cm] = -0.26 ± 0.17 U [cm] = -8.67 ± 0.52 Los Alamos
P056 CA Diff Avg. N [cm] = -0.17 ± 0.15 E [cm] = -1.48 ± 0.20 U [cm] = -21.45 ± 1.55 Porterville
P066 CA Diff Avg. N [cm] = -1.15 ± 0.16 E [cm] = 3.20 ± 0.25 U [cm] = -0.33 ± 0.66
P259 CA Diff Avg. N [cm] = 0.19 ± 0.12 E [cm] = 0.50 ± 0.16 U [cm] = -4.66 ± 0.63
P271 CA Diff Avg. N [cm] = 0.02 ± 0.17 E [cm] = 0.20 ± 0.18 U [cm] = -10.67 ± 0.73 Woodland
P300 CA Diff Avg. N [cm] = 2.08 ± 0.12 E [cm] = 3.67 ± 0.15 U [cm] = 1.17 ± 0.29
P304 CA Diff Avg. N [cm] = 0.93 ± 0.13 E [cm] = 3.60 ± 0.15 U [cm] = -6.76 ± 0.45 Mendota
P307 CA Diff Avg. N [cm] = 0.73 ± 0.20 E [cm] = -1.23 ± 0.27 U [cm] = -13.10 ± 0.93 Madera
P565 CA Diff Avg. N [cm] = -0.77 ± 0.16 E [cm] = -1.06 ± 0.17 U [cm] = -23.45 ± 1.36 Delano
P671 CA Diff Avg. N [cm] = 1.24 ± 0.33 E [cm] = -2.02 ± 0.18 U [cm] = -0.38 ± 0.95
PLSB CA Diff Avg. N [cm] = -2.38 ± 0.13 E [cm] = 0.17 ± 0.13 U [cm] = -19.85 ± 0.38 Woodland
SNI1 CA Diff Avg. N [cm] = 0.61 ± 0.26 E [cm] = -2.05 ± 0.38 U [cm] = 1.37 ± 0.98
Hope this helps to avoid some head scratching from anyone using these CORS. I suspect there nay be others too.
Shelby H. Griggs
CA PLS 6785