which relies on testimony from people on the ground
Actually most park rangers in the Netherlands have a "buitengewone opsporingsbevoegdheid" which means that their testimony, as long as it is within their field of expertise, is admissible as evidence in court, similar to the statements of a police officer.
That's what happened here too. The conviction was purely based on the testimony of those park rangers that wildlife was disturbed by the passing aircraft.