Is there a way to identify the use of a homemade gps jammers?

This is technically possible. Common GPS jammer detection and location measures include:

• By using multiple monitoring points to simultaneously monitor the same interference signal, the location of the interference source can be calculated through a triangulation algorithm based on information such as the direction of arrival. This requires the deployment of a relatively dense network of monitoring equipment in key areas.
• Government agencies can establish public reporting channels for GPS failures and collect and analyze large amounts of user feedback to help determine the scope and pattern of regional jammers gps activity. But the accuracy is relatively low.
• Law enforcement officers can use portable equipment such as radio frequency spectrum analyzers to conduct on-site surveys of areas suspected of interference to more accurately pinpoint the location of the interference source.