WEBVTT

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Hello, I'm Jeff Jalbrzikowski.

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In this video, we will discuss and demonstrate the steps

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you should take before beginning session processing in OPUS Projects.

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Please note, the current version of OPUS Projects may look

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slightly different than what we show here, but its functionality

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generally remains the same.

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So in this training data set, there are 7 marks

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in the project occupied at least two times each.

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Three of them are already in the NGSIDB or integrated

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database, so that means they have permanent IDs or PIDs

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have been assigned to them.

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The three on the left, the other 4 marks with

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the mark IDs only shown on the right will be

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treated as new marks in our training project.

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All three of these marks highlighted have adjusted latitude, longitude,

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and ellipsoid heights from previously submitted GPS projects.

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Two of these marks have adjusted orthometric heights from leveling

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projects and one has a orthometric height from previously submitted

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GPS project.

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So you'll see GPS OBS on its data sheet.

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So in this example or in a project you're working

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on, your new data or this training data here will

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be linked to those existing PIDs.

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Why do we do that?

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We do that for the potential to use those as

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constraints in our network adjustments later.

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And how do we do that?

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Well, there are two ways.

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So let's go over both methods.

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The Upload description window on the left is the primary

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way to link marks.

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It's covered in detail in our Uploading Metadata video.

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If you're following along with our training data set and

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you haven't done that, now before session processing will be

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a good time to revisit it.

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Separately on the right, you can link individual marks to

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PIDs via the Marks page within that data sheet window.

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This can be useful early on in a project, so

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let's take a quick look at that Marks page method.

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If you've already followed along with our video on uploading

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metadata, by uploading the five WinDesc files to your

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project, your marks have already been linked to their respective

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PIDs.

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That process should be considered the primary method for linking

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marks to PIDs, but now we'll walk through the manual

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method.

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We'll start here on the Managers page.

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First, let's navigate to the Marks page for a mark

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that we intend to link to a PID or PID.

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We're now on the Marks page for the mark BRMR.

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Notice the symbology on the map at the top of

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the Marks page.

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The black triangles represent published marks, marks with existing PIDs

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in the NGSIDB.

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The yellow pin represents the mark we're looking at.

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If we hover our cursor over the yellow pin, we'll

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see the mark name in the pop up bubble.

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If we move down slightly and we hover over the

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black triangle, we see a PID.

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If we click the black triangle, a new window will

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open up the Datasheet window.

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To link our new data to this existing mark via

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the PID, we click Use Description and Coordinates.

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We'll see a pop up message telling us that any

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session or Network Solutions may be deleted by this action.

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That's why it's important to ensure that our marks are

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linked to their respective PIDs before session processing.

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When the Marks page completes refreshing, note the changes to

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the color scheme in the map indicating the mark is

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now linked to a PID.

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Notice that some of our description summary has been populated

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with information from the data sheet and down below in

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our processing results, we'll see that our operator coordinate origin

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has changed to reflect that the published value is being

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used in conjunction with velocities calculated by our Horizontal Time

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Dependent Positioning, or HTDP software.

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Now back to our list of all 7 marks in

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the project.

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Four of these marks, the other four are going to

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be treated as if they're new marks that were going

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to be submitting them to be published in the IDB.

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But the secret is, in actuality, they're already in the

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IDB.

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So we're going to go ahead and work through the

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training data as if they are not already blue booked

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marks.

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So these will not be linked.

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OK?

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You're not going to link these.

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Now, in the real world, you would link any new

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data to existing PIDs that you occupy.

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But we're doing this so you are able to compare

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your results to the data sheets to those published positions

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of these marks.

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Remember, these 4 marks will not be linked CORS criteria.

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I like to think of a project as having two

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types of CORS.

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You have your project CORS shown there on the left

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and your distant CORS on the right.

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For your project CORS, you need a bare minimum of

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two.

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One of those will be your hub CORS.

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Ideally, that same CORS will function as your hub for

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all sessions in the project.

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The main purpose of the project CORS is to serve

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as ties to the National Spatial Reference System or NSRS.

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We typically recommend four or five project course.

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More than two can be better, but there is a

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point of diminishing returns.

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If you have 8, 9, 10 CORS in a project, you're spending

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a lot of time looking at results from processing or

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adjustment of those CORS, well, maybe not benefiting all that

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much.

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And over on the right, the distant CORS, you only

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need one and its function is to improve the tropospheric

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modeling in your session processing.

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I sometimes explain it as a Tropo CORS that tends

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to help some people to remember to include it.

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And why.

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Let's briefly go over why we add a distant course

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to every project.

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So our blue cone there represents the GNSS radio signals

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traveling through the atmosphere to our pillar mounted CORS with

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the white radomes and at the same time to our

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orange rovers occupying our project marks.

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The same signals from the same satellites will be received

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by all stations in the diagram.

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Now all of our marks occupied with the rovers in

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orange and our project CORS in the project site, they

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fall within very similar tropospheric conditions.

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We want to remove the effects of the troposphere on

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our processing, but its effects on all six stations on

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the left side of this image are similar.

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So what happens during session processing is that we end

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up cancelling out or zeroing out the tropospheric effects among

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those stations on the left.

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Now, that's good because it's a source of error that

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we've removed, and we have a tropospheric model we can

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use.

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But it's not great because relying solely on the tropospheric

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model can introduce systematic biases in heights and heights are

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important to most GPS projects.

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So to estimate tropospheric correction specific to our data, we

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include one distant CORS in the project and we look

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for that long distance to guarantee that there is a

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different enough tropospheric effect.

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But what we don't want is a vastly different tropospheric

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effect at the distant core site.

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So that would mean we should avoid selecting a distant

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CORS from an area affected by hurricane, large thunderstorms or

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other severely low pressure systems.

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This does not mean that you need to check hourly

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weather data for the entire length of your project, but

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do be aware of those large storms and avoid CORS

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in their path when possible.

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CORS selection.

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Note that all 5 of CORS from each OPUS static

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solution will start out in your project.

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So after uploading our training data, you will have at

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least 5, potentially more CORS in your project, and our

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goal is to narrow that down to four project CORS.

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I'll point out here that the OP user guide explains

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the selection of CORS in detail.

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And don't forget we also need to add the one

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distant CORS.

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As we review the courses in our training project, we

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should keep in mind the three major considerations for Project

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and distant CORS are the same.

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Of course, we want CORS that have data available for

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the duration of the project, and it really is easy

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to determine that in OP you can use the CORS

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selection window.

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Let's take a look at that functionality.

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From the manager's page of our training project.

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We'll click the Add Delete CORS button on the right

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hand side of the map.

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When the CORS selection window has loaded, we can navigate

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the map, click any given CORS and we'll see a

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pop up bubble.

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If we click the Check CORS Data Availability hyperlink, we'll

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get a pop up window that shows the data availability

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profile for that station.

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In the example station here, we see that the data

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is somewhat spotty in a number of days throughout this

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project.

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Let's close the Data Availability window and click the Delete

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or DEL button to add this CORS to the To

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Be Deleted box in the CORS selection window.

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Let's zoom out and move over to look at CORS

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ASUB or A SUB.

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Let's click the Check CORS Data availability hyperlink again and

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we'll note the full coverage shown in the Data availability

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profile.

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Let's close that window and go ahead and click the

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Add button.

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We will add the CORS a sub as our distant

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CORS.

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To complete the selected actions, we must click the Add

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Delete CORS button in the course selection window.

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Within a few moments we should see the managers page

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refresh and if we click the zoom to show all

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CORS Note, we've see that our distant CORS is now

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added to the project.

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There are three types of station velocities that you may

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see in the NCN.

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There's published by the International GNSS Service or IGS.

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They're computed velocities computed by us and NGS.

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And then there are those velocities that we predict using

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the HTDP software.

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You need to have CORS in your projects with published

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or computed velocities.

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So let's take a look at how to confirm this.

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Starting at the NCN homepage, let's enter the site ID

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for CORS NCGA that's in our project.

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Once we land on the station page, we look to

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the left and click the coordinates hyperlink.

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Once that page is loaded, we click the Position and

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velocity hyperlink and finally we land here, where if we

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look at the ITRF velocity, we can see that this

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station has a computed velocity.

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Let's take a quick look at an example of a

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station with a velocity published by the IGS.

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Any CORS with published velocities would be a valuable addition

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to your project.

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And here's a quick glance at a CORS with a

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predicted velocity, which should be avoided in any projects.

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For data quality, we investigate the positional stability of potential

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stations by reviewing the statistics of daily solutions during the

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time span of our project.

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There are two ways to do this.

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If the time span we're interested in is within the

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last 90 days, we can look at the short term

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time series on each station page.

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Let's take a look at where to find those again,

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starting on the NCN homepage, let's enter the site ID

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for CORS VAGP that's in our project.

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Once we land on the station page, we look to

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the left for time series short term, and we click

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that hyperlink.

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Finally, we see the short term time series, often referred

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to as a short term plots.

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Note the three separate plots with daily solutions in northing

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at the top, easting in the middle, and the up

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component at the bottom.

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The X axis of each plot is the day of

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year, while the Y axis shows the centimeters of displacement

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from the published position, which is the red line in

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the middle.

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At the top of the graphic, we see the numeric

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statistics of each positional component.

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Remember that the short term plots access from the station

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page only go back the most recent 90 days.

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Now, if we're past that 90 day window or we

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want to review a custom time period, then we can

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use the NCN Residual Time Series Comparison Tool.

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It's a customizable tool that'll generate a set of statistics

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and graphics that we can download.

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Let's walk through how to use that tool.

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This tool allows us to generate short term plots and

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statistics based on Start Stop dates and a list of

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CORS that we enter.

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Here we will enter dates that span the duration of

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our training project.

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In the box below, we will enter the list of

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CORS that we want to examine.

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Now click the submit button.

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Note the pop up warning that the tool was designed

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to create 90 daytime series, but go ahead and click

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OK.

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When the tool finishes running we can Scroll down and

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we will see a map with color-coded CORS plotted by

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RMS.

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Next we see the summary table of statistics for each

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CORS in our list.

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Below the table are the individual station plots for the

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chosen time span.

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Click the download button to get a zip file that

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contains the summary table and residual time series plots.

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Tropospheric model.

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So the blue curve line here represents an instantaneous continuous

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tropospheric model, right?

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What's actually happening in the atmosphere?

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And so what we're doing is attempting to model that

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in an efficient and accurate way in this session processing.

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So we'll model the troposphere in 7200 seconds or two

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hour intervals, and with a piecewise linear tropo model that's

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simply a series of sloped line segments, each made-up of

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that two hours 7200 second interval, and the endpoints are

00:16:12.220 --> 00:16:13.040
connected.

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And this is what's recommended for submitting your data to

00:16:17.520 --> 00:16:17.800
NGS.

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Note that there is one other option in the Tropo

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model portion of your session processing.

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At this point I'll also mention you can change the

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7200 second interval, but we do recommend keeping the default.

00:16:34.160 --> 00:16:38.180
So the step offset model is a lot like it

00:16:38.270 --> 00:16:38.960
sounds.

00:16:38.960 --> 00:16:41.240
It's these stepped offsets.

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It looks like a set of steps once you sketch

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it out, and they're each 7200 seconds long.

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But the thing that you want to think about is

00:16:51.700 --> 00:16:55.280
that what we're doing here is, is modeling an atmospheric

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correction.

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So we ask ourselves, does nature move in these discrete

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steps like you'd see in the step offset model?

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The answer is no, it really doesn't.

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So remember, it's an atmospheric correction.

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So use the step offset tropo model with caution.

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The elevation cut off.

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So our default elevation cut off in OP is 15°.

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Any observations logged below that 15° angle are excluded from

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our session processing.

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That's a widely accepted standard, so we do recommend sticking

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with the default 15°.

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And I'll briefly mention that OPUS static uses a smaller

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10° mask angle or elevation cut off.

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So we are removing an additional 5° from any observations

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that move on to our session processing constraint weights.

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So there's three options for a constraint weights in session

00:17:56.750 --> 00:17:57.359
processing.

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We have loose, which is about 1m, we have normal

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which is about 1 centimeter and we have tight which

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is 0.1 millimeters of float.

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So our default setting is normal.

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And the reason for that is basically that we know

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CORS data are not perfect, but we don't want to

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use that tight constraint weight because it's effectively 0, you

00:18:24.280 --> 00:18:26.000
know, a 10th of a millimeter.

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We know there's seasonal motion of CORS.

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We want to allow some float amongst those CORS.

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That 10th of a millimeter is so small, we easily

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see more motion than that across even our most stable

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CORS in the network.

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Network design.

00:18:49.040 --> 00:18:52.840
So there's three radio buttons to choose from your network

00:18:52.900 --> 00:18:53.359
design.

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You have user CORS and MST or minimal spanning tree.

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So with User, which is the current default, OPUS Projects

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will actually select a single hub for you.

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Typically it will select the most centrally located CORS, but

00:19:13.440 --> 00:19:17.020
it may select a mark if it has existing published

00:19:17.100 --> 00:19:20.240
geometric position, so do be aware of that.

00:19:20.600 --> 00:19:23.010
This is not only the default in OP, but it's

00:19:23.060 --> 00:19:26.129
also required if you're intending to submit your data to

00:19:26.180 --> 00:19:27.280
us for blue booking.

00:19:27.480 --> 00:19:31.850
The CORS option will select every CORS in the session

00:19:31.930 --> 00:19:35.590
as a hub, and the MST or Minimal Spanning tree

00:19:35.660 --> 00:19:39.560
will select every mark and every chorus as a hub.

00:19:41.040 --> 00:19:44.740
But again, we want you to focus on the default

00:19:44.820 --> 00:19:48.919
in OPUS Projects, especially if you are submitting.

00:19:51.200 --> 00:19:55.600
This module was written and narrated by Jeff Jalbrzikowski and

00:19:55.670 --> 00:19:57.359
recorded in April 2024.

00:19:58.560 --> 00:20:02.440
For further information, please visit the OPUS Projects homepage.