The accuracy studies include stereo satellite data from the following satellites:
- ALOS PRISM
According to Gerry Mitchell, the President of PhotoSat, the company has delivered more than 700 satellite surveying projects since 2007 and accuracy evaluations have been carried out on the majority of them. While most of the actual survey data cannot be publicly published, as that information is proprietary to PhotoSat clients, feedback has been provided on the majority of the projects. The company is able to confirm the results of the 21 new accuracy studies as consistent with both client feedback and the firm’s own project accuracy evaluations.
The accuracy studies were conducted over two test areas: one located west of Asmara, Eritrea, where PhotoSat has access to more than 45,000 ground survey points over a 50 km by 20 km block, and the second in SE California, where PhotoSat uses a very accurate Opentopography.org open source LiDAR survey.
The studies employed different numbers of ground survey control points for each test area and each satellite system, and it was discovered that increasing the number of ground survey points did not necessarily correlate with higher accuracy. For example, the accuracy of the WorldView-3 survey for the California test area was not improved by additional ground survey points. This WorldView-3 survey is accurate to 13 cm in elevation with one ground survey control point and with 153 ground survey control points.
In contrast, some satellite stereo pairs did have accuracy significantly improved by increasing the number of ground survey control points. The WorldView-2 survey for Eritrea was accurate to 19 cm in elevation, with two ground control survey points, and accurate to 14cm in elevation with 21 ground control points. PhotoSat has been continuously producing accuracy studies since 2007 in order to provide objective, quantifiable accuracy data for stereo satellite surveying and mapping. PhotoSat has previously published nine of these studies.