This article focuses on monitoring of a moving disaster area using aerial drones. The aim is to navigate a network of drones to the frontier of the disaster area so that they are able to monitor the faster moving segment of the frontier. A computationally simple sliding-mode control algorithm for navigation of drones is developed. It is proved that the proposed algorithm tracks the moving frontier of the disaster area and achieves the global maximum in the considered optimization problem. Simulations with real bushfire images are conducted to demonstrate the effectiveness of the proposed method.