GPS signal tests of plastic samples

Summary of the Experiment

This page describes an experiment conducted to see whether any of the plastics we are considering for use in the SCIGN radomes would effect the GPS signal less or more than others tested. We obtained samples of Lexan, Xenoy and Geloy from GE Plastics. Each sample tested was a 6" x 8" piece of 1/8" (0.125") thick plastic. These plastics are described in more detail in an earlier report on their general properties.

Our simple test involved placing the samples over a GPS antenna for 2 hours each. This was performed on station NMD1. A short baseline to a second station on an identical antenna mount, and with identical receiver and antenna (and firmware) was occupied during the test. The 'reference station' for the test is named NMUD. The antenna mounts are 'rock pins' drilled into the roof parapet wall of the North Mudd building at Caltech. The antennas are Ashtech Dorne-Margolin choke ring (DMCR), and the receivers are Ashtech Z-12's. Another short baseline is available to existing SCIGN station CIT1 , only a few meters away, but with a different antenna mount and AOA turborogue receiver and AOA DMCR antenna. Data from that receiver are in the SCIGN archive and available for this time from the SCIGN archive at SIO. Photos of the experiment setup are available here .

Preliminary results indicate that each of the samples tested allows the GPS signal to pass through with about the same high degree of transparency. None of the plastics tested seem to cause any serious problems in the ability to estimate these short baselines very precisely, even with just the two hours of data for each. In terms of tracking, the autcln summary files for intervals of the short (2-hour) sample tests indicate that there is no noticable difference between stations NMUD and NMD1. That is, it's as if the plastic samples are not even there. Some of the plastic samples appear to cause minor jumps in the vertical apparent phase center, but these could be just random error (maybe Geloy produces a barely significant difference).

Here is a list of the samples tested:

Number  Type    Grade   Appearance      Sample  Comments
------  -----   ------  ----------      ------  --------
1.      Lexan   143     clear           plaque  medium flow
2.      Lexan   HF1130  clear           plaque  higher flow than #1
3.      Xenoy   2230EU  black           plaque  stronger than #4 or #5 
4.      Xenoy   2730EU  green           plaque  (weaker than #3)
5.      Xenoy   1731    black           plaque  low water absorption 
6.      Geloy   XP2003  white           plaque  (#6 and #7 are of the
7.      Geloy   XP2003  lt. tan         circle     same material)

Because samples #6 and #7 are identical material, only #6 was tested.

Problems identified so far with how the test was conducted:

• 1) The NMUD Z-12 was being used simultaneously for RTK tests and had at least one firmware setting set differently than on NMD1. Apparently NMUD had 'clock steering' or 'interpolation' turned OFF, whereas NMD1 had it turned ON. This was not intentional, and was only recognized during data post-processing.

• 2) On day 058, after the Lexan (clear) samples were tested, we then tested sample #3 (opaque, black) - when removing this sample we noticed that the fiberglass tape had been placed so that it overlapped the alum. cylinder sidewalls below (such that near the E and W edges, the GPS signal was passing through the fiber tape as well as through the plastic. The photos were taken of sample #1, and show how the tape was supposed to be positioned for all samples. At worst, it was not done quite right for samples #2 and #3, but it was done right for samples #1, #4, #5, and #6.

Data and Observation Schedule

Here is the schedule of observations during the experiment, along with data files split out for each sub-daily time interval of interest. If you prefer, here are files for NMD1 for days 0580 and 0610 that have not been split up into segments (times are listed below so that you can compare the plastic samples).

There are summary files showing contents of each RINEX file here .

Please write to me with any questions if this is not entirely clear as presented here.

RINEX data files from station NMD1:

• Day 0560 0220-2400 GMT (no antenna cover, plain)
• Day 0570 0000-2400 GMT (no antenna cover, aluminum sleeve in place)
• Day 0580 0000-1645 GMT (no antenna cover, aluminum sleeve in place)
  0581 - 1645-1840 GMT - plastic sample #1 mounted on top of alum. sleeve
  0582 - 1845-2055 GMT - plastic sample #2 mounted on top of alum. sleeve
  0583 - 2105-2345 GMT - plastic sample #3 mounted on top of alum. sleeve
  
• Day 0590 0000-2400 GMT (thermoformed lexan dome on, alum. sleeve on)
• Day 0600 0000-2400 GMT (thermoformed lexan dome on, alum. sleeve on)
• Day 0610 0000-1720 GMT (thermoformed lexan dome on, alum. sleeve on)
  0614 - 1720-1910 GMT - plastic sample #4 mounted on top of alum. sleeve
  0615 - 1920-2115 GMT - plastic sample #5 mounted on top of alum. sleeve
  0616 - 2125-2315 GMT - plastic sample #6 mounted on top of alum. sleeve
  
• Day 0620 0000-2400 GMT (no antenna cover, plain)
• Day 0630 0000-2400 GMT (no antenna cover, plain)

RINEX data files from station NMUD:

• Day 0560 full data file (no antenna cover, plain)
• Day 0570 full data file (no antenna cover, plain)
• Day 0580 full data file (no antenna cover, plain)
• Day 0590 full data file (no antenna cover, plain)
• Day 0600 full data file (no antenna cover, plain)
• Day 0610 full data file (no antenna cover, plain)
• Day 0620 full data file (no antenna cover, plain)
• Day 0630 full data file (no antenna cover, plain)

Processing Results:

At this point, we've made first-cut runs of all data from the experiment, processing daily solutions (0000-2400 GMT) for each day. We've also run the data segments during the 2-hour tests for each sample.

Section 1. - Daily solution results

Using GAMIT (in LC_HELP mode), the daily solutions have all been processed satisfactorily for all days of the experiment: (each is linked to the backed-up solution directory)

056 : 057 : 058 : 059 : 060 : 061 : 062 : 063

Here are some bias-fixed baseline output summaries: basically all of the data appear to be processing just fine. The aluminum sleeve introduces a vertical shift in apparent phase center of station NMD1 of some 50-60 mm (see day 056 to day 057 change in U [up-down] component). Baseline component numbers are reported in meters.

At this stage, the day 057 solution (with 'outliers' in components of NMUD) is the only one with a significantly higher solution rms (about twice as high as for other days) - we'll likely be re-running all of these solutions [note: latest re-run still shows problems with the solution for day 057].

otiesa.056:NMD1_NMUD 1998.056X N       -2.6694 +-   0.0025 E       -0.0358 +-   0.0021 U       -0.0049 +-   0.0058 L        2.6697 +-   0.0025  Correlations (N-E,N-U,E-U) =    0.06170  -0.15608   0.04388
otiesa.057:NMD1_NMUD 1998.057X N       -2.6550 +-   0.0022 E       -0.0060 +-   0.0023 U       -0.0698 +-   0.0049 L        2.6560 +-   0.0021  Correlations (N-E,N-U,E-U) =    0.15596  -0.16211  -0.14349
otiesa.058:NMD1_NMUD 1998.058X N       -2.6710 +-   0.0020 E       -0.0370 +-   0.0019 U       -0.0630 +-   0.0045 L        2.6720 +-   0.0020  Correlations (N-E,N-U,E-U) =    0.07019  -0.08313   0.04851
otiesa.059:NMD1_NMUD 1998.059X N       -2.6709 +-   0.0020 E       -0.0381 +-   0.0019 U       -0.0575 +-   0.0042 L        2.6718 +-   0.0020  Correlations (N-E,N-U,E-U) =    0.12593  -0.10880  -0.01307
otiesa.060:NMD1_NMUD 1998.060X N       -2.6704 +-   0.0019 E       -0.0382 +-   0.0019 U       -0.0578 +-   0.0040 L        2.6713 +-   0.0019  Correlations (N-E,N-U,E-U) =    0.14996  -0.17287  -0.02217
otiesa.061:NMD1_NMUD 1998.061X N       -2.6720 +-   0.0020 E       -0.0382 +-   0.0021 U       -0.0623 +-   0.0046 L        2.6730 +-   0.0020  Correlations (N-E,N-U,E-U) =    0.12102  -0.14674  -0.06986
otiesa.062:NMD1_NMUD 1998.062X N       -2.6701 +-   0.0022 E       -0.0371 +-   0.0020 U       -0.0560 +-   0.0046 L        2.6709 +-   0.0022  Correlations (N-E,N-U,E-U) =    0.01487  -0.12685   0.08607
otiesa.063:NMD1_NMUD 1998.063X N       -2.6709 +-   0.0021 E       -0.0381 +-   0.0020 U       -0.0573 +-   0.0047 L        2.6718 +-   0.0021  Correlations (N-E,N-U,E-U) =    0.12443  -0.10762  -0.06817

otiesa.056:CIT1_NMUD 1998.056X N       -6.0469 +-   0.0025 E       -0.3221 +-   0.0022 U        0.0876 +-   0.0059 L        6.0561 +-   0.0026  Correlations (N-E,N-U,E-U) =    0.08336  -0.17833   0.00176
otiesa.057:CIT1_NMUD 1998.057X N       -6.0325 +-   0.0022 E       -0.2917 +-   0.0024 U        0.0825 +-   0.0050 L        6.0402 +-   0.0022  Correlations (N-E,N-U,E-U) =    0.19282  -0.17758  -0.18336
otiesa.058:CIT1_NMUD 1998.058X N       -6.0472 +-   0.0022 E       -0.3222 +-   0.0021 U        0.0876 +-   0.0047 L        6.0564 +-   0.0022  Correlations (N-E,N-U,E-U) =    0.08875  -0.09048  -0.00715
otiesa.059:CIT1_NMUD 1998.059X N       -6.0477 +-   0.0020 E       -0.3220 +-   0.0020 U        0.0864 +-   0.0043 L        6.0568 +-   0.0021  Correlations (N-E,N-U,E-U) =    0.16644  -0.15074  -0.05892
otiesa.060:CIT1_NMUD 1998.060X N       -6.0478 +-   0.0019 E       -0.3215 +-   0.0019 U        0.0882 +-   0.0042 L        6.0570 +-   0.0020  Correlations (N-E,N-U,E-U) =    0.16584  -0.15898  -0.05521
otiesa.061:CIT1_NMUD 1998.061X N       -6.0485 +-   0.0021 E       -0.3208 +-   0.0022 U        0.0857 +-   0.0047 L        6.0576 +-   0.0021  Correlations (N-E,N-U,E-U) =    0.15630  -0.16512  -0.10501
otiesa.062:CIT1_NMUD 1998.062X N       -6.0472 +-   0.0023 E       -0.3211 +-   0.0021 U        0.0882 +-   0.0047 L        6.0563 +-   0.0023  Correlations (N-E,N-U,E-U) =    0.04107  -0.13572   0.01833
otiesa.063:CIT1_NMUD 1998.063X N       -6.0482 +-   0.0022 E       -0.3220 +-   0.0021 U        0.0869 +-   0.0049 L        6.0574 +-   0.0022  Correlations (N-E,N-U,E-U) =    0.16252  -0.12647  -0.12873

otiesa.056:CIT1_NMD1 1998.056X N       -3.3774 +-   0.0020 E       -0.2862 +-   0.0019 U        0.0925 +-   0.0044 L        3.3908 +-   0.0020  Correlations (N-E,N-U,E-U) =    0.05812  -0.16661  -0.00029
otiesa.057:CIT1_NMD1 1998.057X N       -3.3775 +-   0.0017 E       -0.2857 +-   0.0017 U        0.1523 +-   0.0037 L        3.3930 +-   0.0017  Correlations (N-E,N-U,E-U) =    0.12986  -0.17237   0.00894
otiesa.058:CIT1_NMD1 1998.058X N       -3.3761 +-   0.0018 E       -0.2852 +-   0.0019 U        0.1506 +-   0.0039 L        3.3915 +-   0.0018  Correlations (N-E,N-U,E-U) =    0.09124  -0.15495   0.04593
otiesa.059:CIT1_NMD1 1998.059X N       -3.3768 +-   0.0017 E       -0.2839 +-   0.0017 U        0.1439 +-   0.0036 L        3.3918 +-   0.0017  Correlations (N-E,N-U,E-U) =    0.11745  -0.17918  -0.00113
otiesa.060:CIT1_NMD1 1998.060X N       -3.3774 +-   0.0017 E       -0.2833 +-   0.0016 U        0.1459 +-   0.0037 L        3.3924 +-   0.0017  Correlations (N-E,N-U,E-U) =    0.12496  -0.15249  -0.05495
otiesa.061:CIT1_NMD1 1998.061X N       -3.3765 +-   0.0017 E       -0.2826 +-   0.0018 U        0.1480 +-   0.0037 L        3.3915 +-   0.0017  Correlations (N-E,N-U,E-U) =    0.13339  -0.18311  -0.04196
otiesa.062:CIT1_NMD1 1998.062X N       -3.3771 +-   0.0018 E       -0.2840 +-   0.0018 U        0.1442 +-   0.0038 L        3.3921 +-   0.0018  Correlations (N-E,N-U,E-U) =    0.06762  -0.16453   0.00945
otiesa.063:CIT1_NMD1 1998.063X N       -3.3773 +-   0.0017 E       -0.2839 +-   0.0017 U        0.1442 +-   0.0038 L        3.3923 +-   0.0017  Correlations (N-E,N-U,E-U) =    0.13443  -0.18043  -0.05057

Section 2. - Solutions for 2-hour data subsets for each plastic sample

Here are some initial results of baseline processing (in L1, L2 independent mode) for the individual plastics samples:

Sample #1 (058) NMD1_NMUD 1998.058X N       -2.6696 +-   0.0006 E       -0.0338 +-   0.0005 U       -0.0250 +-   0.0013 L        2.6699 +-   0.0006  Correlations (N-E,N-U,E-U) =    0.06338  -0.14655  -0.22827
Sample #2 (058) NMD1_NMUD 1998.058X N       -2.6703 +-   0.0005 E       -0.0349 +-   0.0006 U       -0.0256 +-   0.0011 L        2.6706 +-   0.0005  Correlations (N-E,N-U,E-U) =   -0.00527   0.01836   0.24978
Sample #3 (058) NMD1_NMUD 1998.058X N       -2.6695 +-   0.0005 E       -0.0345 +-   0.0005 U       -0.0246 +-   0.0013 L        2.6699 +-   0.0005  Correlations (N-E,N-U,E-U) =    0.27784  -0.10870  -0.23887
Sample #4 (061) NMD1_NMUD 1998.061X N       -2.6695 +-   0.0006 E       -0.0330 +-   0.0006 U       -0.0256 +-   0.0013 L        2.6698 +-   0.0006  Correlations (N-E,N-U,E-U) =   -0.06105  -0.17844  -0.05708
Sample #5 (061) NMD1_NMUD 1998.061X N       -2.6703 +-   0.0007 E       -0.0351 +-   0.0007 U       -0.0250 +-   0.0014 L        2.6707 +-   0.0007  Correlations (N-E,N-U,E-U) =    0.32363  -0.27794  -0.18427
Sample #6 (061) NMD1_NMUD 1998.061X N       -2.6694 +-   0.0006 E       -0.0346 +-   0.0005 U       -0.0234 +-   0.0016 L        2.6698 +-   0.0006  Correlations (N-E,N-U,E-U) =    0.26583  -0.11633  -0.24949

Sample #1 (058) CIT1_NMUD 1998.058X N       -6.0476 +-   0.0007 E       -0.3158 +-   0.0006 U        0.0908 +-   0.0016 L        6.0565 +-   0.0007  Correlations (N-E,N-U,E-U) =    0.20384  -0.34260  -0.37733
Sample #2 (058) CIT1_NMUD 1998.058X N       -6.0475 +-   0.0006 E       -0.3159 +-   0.0006 U        0.0896 +-   0.0013 L        6.0564 +-   0.0006  Correlations (N-E,N-U,E-U) =    0.08626   0.01062   0.03490
Sample #3 (058) CIT1_NMUD 1998.058X N       -6.0474 +-   0.0005 E       -0.3157 +-   0.0005 U        0.0900 +-   0.0013 L        6.0563 +-   0.0005  Correlations (N-E,N-U,E-U) =    0.26879  -0.07193  -0.22966
Sample #4 (061) CIT1_NMUD 1998.061X N       -6.0474 +-   0.0006 E       -0.3153 +-   0.0006 U        0.0894 +-   0.0013 L        6.0562 +-   0.0006  Correlations (N-E,N-U,E-U) =   -0.06243  -0.18584  -0.04983
Sample #5 (061) CIT1_NMUD 1998.061X N       -6.0484 +-   0.0007 E       -0.3164 +-   0.0008 U        0.0910 +-   0.0017 L        6.0574 +-   0.0008  Correlations (N-E,N-U,E-U) =    0.42604  -0.38999  -0.37852
Sample #6 (061) CIT1_NMUD 1998.061X N       -6.0476 +-   0.0006 E       -0.3157 +-   0.0005 U        0.0904 +-   0.0016 L        6.0565 +-   0.0006  Correlations (N-E,N-U,E-U) =    0.28020  -0.07004  -0.22097

Sample #1 (058) CIT1_NMD1 1998.058X N       -3.3780 +-   0.0007 E       -0.2819 +-   0.0006 U        0.1158 +-   0.0016 L        3.3917 +-   0.0007  Correlations (N-E,N-U,E-U) =    0.20352  -0.34291  -0.37760
Sample #2 (058) CIT1_NMD1 1998.058X N       -3.3772 +-   0.0006 E       -0.2810 +-   0.0006 U        0.1153 +-   0.0013 L        3.3909 +-   0.0006  Correlations (N-E,N-U,E-U) =    0.08626   0.01062   0.03490
Sample #3 (058) CIT1_NMD1 1998.058X N       -3.3778 +-   0.0005 E       -0.2812 +-   0.0005 U        0.1146 +-   0.0013 L        3.3915 +-   0.0005  Correlations (N-E,N-U,E-U) =    0.26879  -0.07193  -0.22966
Sample #4 (061) CIT1_NMD1 1998.061X N       -3.3779 +-   0.0006 E       -0.2823 +-   0.0006 U        0.1150 +-   0.0013 L        3.3916 +-   0.0006  Correlations (N-E,N-U,E-U) =   -0.06243  -0.18584  -0.04983
Sample #5 (061) CIT1_NMD1 1998.061X N       -3.3781 +-   0.0007 E       -0.2813 +-   0.0008 U        0.1160 +-   0.0017 L        3.3918 +-   0.0008  Correlations (N-E,N-U,E-U) =    0.42604  -0.38999  -0.37852
Sample #6 (061) CIT1_NMD1 1998.061X N       -3.3782 +-   0.0006 E       -0.2811 +-   0.0006 U        0.1138 +-   0.0016 L        3.3917 +-   0.0007  Correlations (N-E,N-U,E-U) =    0.27257  -0.05945  -0.22357

These reports are preliminary and have not been reviewed for conformity with U. S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive use only and does not imply endorsement by the U. S. Government.

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