SatSCADA SAT1xx terminals operate on the Inmarsat IsatData Pro Satellite network.  For proper operation, SatSCADA SAT1xx satellite terminals must have clear line of site path to the satellite.

This document shows the process of analysis and testing for satellite line of site with SAT1xx terminals  for a remote site requiring satellite  connectivity.

The Inmarsat IsatData Pro operaties on the I-4 satellite network consist of  3 Geosynchronous satellites located 22,199 miles above the equator. Operation in North  American is covered by the I-4 F3 satellite at 97.6W.  The elevation and azimuth angle to the satellite will depend on the location of the satellite terminal relative to the Inmarsat Satellite. Elevation and Azimuth Angles for North American sites are shown in Table 1 – with elevations ranging for 24.2  degrees in Northern Alberta to 54.2 degrees in Florida.  To achieve line of site, the satellite path must also clear terrain and man-made obstruction in the satellite path as shown in figure 1. 

The IsatData Pro network operates in the L-Band which is impervious to the effects of rain, fog or snow; so given a good satellite line of site, the omni directional SAT1xx terminal will operate without  requirement for antenna pointing. The picture on the right shows a SAT100 terminal located atop a  pipe mast on the SAT100 RTU setup.

Figure 1  – Satellite Elevation Angle vs Terrain Obstruction Angle

A – Elevation Angle to Satellite at Remote Site

B – Elevation Angle to Obstruction Calculated from Height and Distance to Near Obstruction

H = Height of Obstruction

D = Distance to Obstruction

For Satellite Clearance   A > B

Satellite Line of Site Analysis / Testing Example for Remote Site

Preliminary Analysis for Remote Site West of Calgary, Alberta, Canada

There was a requirement for remote connectivity for a hydrological monitoring site (creek flow and level)  located in the mountains west of Calgary.

The site does not have reliably terrestrial communications, so use of SatSCADA Inmarsat based satellite communication solutions was assessed. The remote site was located in a valley. The line of site path from the site to the satellite had an elevations angle of 29.5 degrees and azimuth of 159.2 degrees South of North to satellite. The path was pointing south through the valley as shown in the top 2 images.

As seen from Table 1 the look angle from the  site to the Inmarsat satellite (satellite is located at the equator at a mean elevation of 22,199 miles above mean sea level)  has an elevation angle of  29.5 degrees above the horizon. Preliminary analysis of the  line of site path compared to the terrain indicated that the path should be clear however in a rugged terrain near near obstruction from foliage and terrain may obstruct the path, so onsite visit and  field tests were performed to verify the satellite communications path.

Image 3 – View of Site looking from the Southwest

Image 4 – View Looking South

Image 4 and shows the site  looking  south and appears to be clear with the exception of foliage and gentle slope (Image 2). Image 3 shows the rugged terrain. If site was located north its satellite view would be obstructed by mountains.

Site Visit & Field Testing with SAT110 Satellite Terminal

Observations

The remote site was located in a clearing on plateau in a valley between large mountains. The site visit  found that the line of site path looking south to the satellite appeared clear, however there are 60 foot high trees (H) beginning at about 120 feet away (D) along the path. The estimated obstruction angle (B ) with trees at this distance (D)  is about be 26 degrees. Based on this obstruction angle the satellite path should clear.

Field Testing

We performed site testing using a SAT110 Terminal, since the SAT110 terminal is battery powered, making it easy to use for testing. The SAT110 terminal placed on the ground for testing by the site had successful communications, confirming path clearance. The satellite terminal can be mounted higher  on a small pipe mast or tower (i.e.  10-20′ high) and/or  located further back from the creek to provide additional path clearance.

Conclusion

Satellite line of site path analysis can comprise of both analytical study as well as field testing. A preliminary analytic study is always recommended in rugged terrain to verify if the path is even viable. For example if the remote site was located on the other side of the mountains, there would be no possibility of a line of site satellite path. In rugged terrain with tree cover, a site visit is recommended to verify clearance from foliage.

As one can see from Table 1 the elevation angle and the azimuth angle from the site to the satellite can dramatically affect the line of site. The look angle to the site becomes steeper as the site get closer to the equator, allowing for better path clearance. Conversely northern sites have lower elevation look angles.

For sites with line of site path to the satellite, the Inmarsat  network will provide high reliable and  always on connectivity.  This example shows the process how Inmarsat connectivity can be verified for operations at remote sites.

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