The pilot reported that during an aerial observation flight he finished the survey block and decided to land at an airport nearby to use the restroom and get fuel. He reported that he had never been to the airport, so he chose to enter the traffic pattern “a little high” as he noticed terrain around the airport. On final approach, the pilot executed a forward slip maneuver to reduce “excess airspeed and altitude” and once over the runway, he entered the landing flare, and the airplane floated down the runway about 500 ft. Subsequently, the airplane touched down nose first and entered a porpoise, which resulted in the collapse of the nose landing gear and a runway excursion through the end of the runway. The airplane sustained substantial damage to the fuselage and left wing. The passenger on-board, who was the sensor operator, reported that while on short final approach, he observed the airspeed to be 125 knots, with a descent rate of 1,250 feet per minute, and the airplane subsequently touched down ”halfway down” the runway. He then described that the airplane began to porpoise, and the pilot retracted the landing gear and applied full power, however the airplane ”hit the ground” again and slid off the runway. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.