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Original file line number | Diff line number | Diff line change |
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# daily_avg<a name="module5"></a> | ||
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Updated August 10, 2023 by Kristine Larson | ||
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<code>daily_avg</code> is a utility for people interested | ||
in daily averaged reflector heights, such as are used for measuring | ||
snow accumulation or water levels in lakes/rivers. *It is not to be used for tides!* | ||
The goal is to make a valid daily average - for this reason, we have two required inputs | ||
for quality control. | ||
There are two required inputs for quality control. | ||
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- The first is called a *median filter* value. This input helps remove | ||
large outliers. For each day, a median RH is found. Then all values larger than the | ||
*median filter* value from the median RH are thrown out. | ||
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- The second required input to <code>daily_avg</code> sets a limit for how | ||
- The second required input *ReqTracks* sets a limit for how | ||
many satellite arcs are considered sufficient to create a trustworth daily average. | ||
If you had 5 arcs, for example, you probably would not want to compare that | ||
with another day where 100 arcs were available. The number of tracks required | ||
varies a lot depending on the azimuth mask and the number of frequencies available. | ||
If you are not sure what values to use at your GNSS site, run it once with very minimal constraints. | ||
The code provides some feedback plots that will let you pick better values. | ||
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Note: the computed daily average value should be associated with 12:00 UTC, not midnight. | ||
Notes: | ||
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- the computed daily average value should be associated with 12:00 UTC, not midnight. | ||
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Here is an example from one of our use cases where there are a few large outliers. | ||
I have set the median filter value to 2 meters and the required number of tracks to 12: | ||
- If you are interested in looking at subdaily variations of reflector height, you should | ||
be using subdaily. | ||
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<code> daily_avg mchn 2 12 </code> | ||
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You can easily see the outliers. | ||
The outputs: | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn-A.png> | ||
</p> | ||
- completely raw RH that have been concatenated into a single file. The location of the file | ||
is printed to the screen and a plot is created. | ||
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Is 12 a good choice? The code also prints out a plot telling you how many | ||
tracks are available each day: | ||
- all RH that meet the QC criteria | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_nvals.png> | ||
</p> | ||
- daily average RH that meet the QC criteria | ||
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These can vary quite a bit by year as the station operators change receivers and/or | ||
tracking strategies. You should pick the values that are best for your experiment. | ||
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I illustrate the steps you might take with station MCHN. The antenna is very close to the water, so that is | ||
But the receiver itself is operated suboptimally and only L1 GPS data can be used here. | ||
This severely limits the number of tracks that can be used. | ||
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Next I have rerun the code with a better median filter constraint of 0.25 meters: | ||
I start out with almost no QC (outliers with 2 meters of the median value, only 5 satelliet arcs required per day): | ||
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<code> daily_avg mchn 0.25 12 </code> | ||
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<code> daily_avg mchn 2 5 </code> | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn-B.png> | ||
<img width=500 src=../_static/mchn_01.png> | ||
</p> | ||
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Since this documentation was written, I have added the median value to the plots: | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_tighter.png> | ||
<img width=500 src=../_static/mchn_02.png> | ||
</p> | ||
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If you still are finding it challenging to see the variations from the median value, you | ||
can try setting the plot_limits option: | ||
<p align=center> | ||
<img width=500 src=../_static/mchn_03.png> | ||
</p> | ||
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<code> daily_avg mchn 0.25 12 -plot_limits T </code> | ||
You can easily see the outliers - and that you need to use something more | ||
useful than 2 meters for the median filter. I will use 0.25 meters. I am also going to | ||
change the required tracks to 10 | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_wlimits.png> | ||
<img width=500 src=../_static/mchn_04.png> | ||
</p> | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_05.png> | ||
</p> | ||
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The daily average plot: | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn-C.png> | ||
<img width=500 src=../_static/mchn_06.png> | ||
</p> | ||
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Two txt files are created. One has all the tracks that fit the QC. The other has the desired daily | ||
average. The location of the files is printed to the screen. You are welcome to generate your | ||
own quality control codes for the daily average if you find this one does not meet your purposes. | ||
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Updated August 10, 2023 | ||
There is also an optional plot_limits setting so you can see how close the variation of | ||
the measurements is with respect to your choices. I will also tighten the median filter a bit: | ||
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<code> daily_avg mchn 0.20 10 -plot_limits T </code> | ||
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You can see that at least visually, this makes no change in the daily averages. | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_07.png> | ||
</p> | ||
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<p align=center> | ||
<img width=500 src=../_static/mchn_08.png> | ||
</p> | ||
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Kristine M. Larson | ||
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@@ -40,7 +40,7 @@ | |
] | ||
setup( | ||
name="gnssrefl", | ||
version="1.4.9", | ||
version="1.5.0", | ||
author="Kristine Larson", | ||
author_email="[email protected]", | ||
description="A GNSS reflectometry software package ", | ||
|