GNSS Denied Environments
Every now and then, we are required to conduct operations in GNSS (Global Navigation Satellite System) Denied environments. These operations typically carry with them a higher level of risk as there are normally other complications such as flying indoors, inconsistent air flows, low levels of light or very tight clearances. Other times we can be in GNSS denied environments include, in a city canyon, in a deep valley or at the bottom of an open pit mine. There can also be anomalies in any of the GNSS constellations which includes deactivation of a constellation by the GNSS operators. In most cases (apart from areas that we expect to have no GNSS reception) the pilot will suspend the operation until we can regain a position lock.
These GNSS denied environments don’t just prevent the pilot from being able to hold position, but also generally prevents automated flight paths such as being used in Survey style operations or ensuring the operation is consistently capturing the same data over time (Asset Inspection etc.). There are a number of systems that are available to allow us to continue to hold position and or navigate in GNSS denied environments, this includes: Optic Flow, SLAM, Radar, Ultra Wide Band Localisation, proximity sensors or dead reckoning. A handful of our multirotor platforms have Optic Flow but must be in relatively well lit areas with distinguishable features on the ground to work efficiently. In most cases, a highly experienced pilot and an efficient crew are the best ways to handle GNSS denied environments and still achieve survey data sets.
During our drone training courses, we expose all of our students to a GNSS denied environment where they can quickly reactivate the GNSS if required. During the rpas training we will also show them how to return to the home location in the event of a GNSS failure. This quickly teaches the students how to operate the system without relying on the autopilot, and bring it home in the event of a single failure.
Image sourced from: NASA – [dead link], Public Domain, https://commons.wikimedia.org/w/index.php?curid=564265