Three test sites, each site serving a particular purpose, were used for all of the SUAV Auto GCAS flight tests. Figure 32 provides an aerial map view of the three test sites.
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The coordinates for each test site are provided to enable readers to find those locations on Google Earth (Google Inc., Mountain View, California). In each case, the coordinates represent the approximate position of the ground control van as shown in the figure for that site.
The North Base test site lies at 34° 59.400’ north latitude and 117° 51.890’ west longitude. The North Base test site was the closest location to AFRC and therefore required the least amount of logistical effort for test team deployment. This site was also selected because it was where normal DROID operations had previously been accomplished. The North Base test site was one of the locations within EAFB airspace that had been approved for SUAV operations (as coordinated through the normal flight-test scheduling process).
The North Base test site had the advantage of an existing hard-surface runway (fig. 33). From an Auto GCAS point of view, the North Base test site was limited to smooth-terrain test points because the entire area is quite flat.
Figure 33. North Base test site.
The first few characterization flights and functional check-flights were accomplished at the North Base test site location. The Auto GCAS component functions were also verified at this test site. One of the North Base test site flights included the first few smooth-terrain Auto GCAS test points.
The Rosamond Lakebed test site lies at 34° 52.132’ north latitude and 118° 5.200’ west longitude. The Rosamond Lakebed test site offered the slight advantage of small terrain features that could provide Auto GCAS test options other than those provided by the predominantly smooth terrain of the North Base test site. The main advantage of the Rosamond Lakebed test site was that the logistics of test team deployment were much simpler than what would have been required to deploy the test team to a remote desert location.
53 There is a small hill (approximately 75 ft tall) on the north side of the lakebed. That hill was used as the location for the first few Auto GCAS test points over terrain that was not smooth (fig. 34). The safety pilot was located at the top of that hill for those test points.
Figure 34. Rosamond Lakebed test site.
The Rosamond Lakebed test site offered no hard surface runway, but the lakebed surface was normally dry enough to support DROID takeoff and landing operations. This test site was another of the locations within EAFB airspace that had been approved for SUAV operations (as coordinated through the normal flight-test scheduling process).
The GCAS Valley test site lies at 35° 12.208’ north latitude and 117° 25.116’ west longitude. The GCAS Valley test site was selected because it provided a very useful variety of terrain features, and because one of the small lakebeds within it provided an adequate takeoff and landing surface for the DROID. The specific test locations within the GCAS Valley test site (fig. 35) were selected in order to provide adequate areas in which to position the safety pilot and ground observers.
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The GCAS Valley test site required the most logistical effort for test team deployment. This test site was only reached after almost two hours of driving time from AFRC; approximately half of that time spent driving on partially-maintained dirt roads. This test site was located directly underneath the Black Mountain low-altitude supersonic corridor, and required special scheduling to avoid airspace conflicts with other flight-test operations. On each test day, a Notice to Airmen (NOTAM) was issued to alert other pilots to the DROID test activity in that area.
The test area closest to Fremont Peak was about 1.5 miles from the lakebed used for takeoff and landing. It required an additional 30-45 minutes to move the safety pilot and ground observers to their assigned stations via rough dirt roads.
Despite the logistical challenges, this test site was well-suited for Auto GCAS flight testing on the DROID class of aircraft. Almost all SUAV Auto GCAS flight-testing was accomplished at the GCAS Valley test site. This test site included smooth terrain; a small hill (approximately 350 ft taller than the surrounding terrain) with safety pilot access to the top of that hill; moderate terrain (approximately 700 ft taller than the surrounding terrain) including a small box canyon with safety pilot access on the side of that canyon; and a small saddle area for nuisance testing.
Ground Survey at the GCAS Valley Test Site
An important consideration for the GCAS Valley test site was whether or not the terrain features were actually at the same longitude, latitude, and altitude positions as those indicated by the DEM within the NED. The answer was not considered a flight-safety issue because the safety pilot remained the primary protection against ground impact. However, a technical problem could have arisen if the actual terrain in the GCAS Valley were significantly different than that as shown by the NED, so a ground survey for key terrain features within the GCAS Valley was conducted.
Ground surveys have been a common procedure on past Auto GCAS flight-test projects. On the F-16 Auto GCAS projects in the 1990s and portions of the F-16 FRRP, ground surveys were accomplished by project personnel hiking to the relevant terrain features with handheld GPS units. This same technique was also used for the SUAV Auto GCAS project in the GCAS Valley for the valley floor and the accessible sides of the hills (only where the terrain was not too steep to walk).
One of the test sites used by the F-16 FRRP included terrain that was much too steep for simple hiking surveys. At that test site the professional surveyors at the NGA were requested to accomplish a more formal survey. These NGA surveyors were already stationed at EAFB and conducted surveys like this as a normal part of their support for base activities. For inaccessible terrain locations these surveyors used standard triangulation techniques to obtain high accuracy.
The NGA was also requested to support the SUAV Auto GCAS project by surveying the more inaccessible portions of the GCAS Valley. From an Auto GCAS perspective it was not necessary to obtain a ground survey in a rectangular grid for the entire area; it was only necessary to survey the ridgelines at the planned test sites within the GCAS Valley. The ridgelines were the most likely areas to trigger an avoidance maneuver, and were also the areas where it was most likely for the test aircraft to get closest to terrain (during or shortly after the avoidance maneuver).
Figure 36 shows the results of the NGA survey for a portion of the small box canyon area. The bottom cusp of each white balloon represents the survey altitude at that longitude and latitude. The white line below each balloon represents the difference between the survey altitude and the Google Earth representation.
55 Figure 36. NGA survey at primary test area.
The Google Earth graphics were also based on NED data, and figure 36 is considered a good depiction of the altitude errors that would be inherent to the Auto GCAS algorithm that was also based on NED data. Figure 37 provides an overall summary of the difference between the NGA survey and the NED data at the closest NED post to the survey coordinates.
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The histogram data shown in figure 37 indicate that the survey data were higher than the nearest NED post by about 27 ft on average. One survey point was approximately 60 ft higher than the corresponding NED post. There were no cases in which the NGA survey data were below the NED data.
The overall conclusion from the NGA survey was that the NED data were sufficiently accurate to provide a viable source for the Auto GCAS algorithm. The 27-ft average error was within the tolerance provided by the DEM uncertainty buffer of 30 ft. The scan pattern methodology and the selection of DEM posts outside the scan pattern (fig. 28) provided sufficient additional buffering.