What technique requires simultaneous GPS observations at a known position for corrections?

The technique that requires simultaneous GPS observations at a known position for corrections is Differential GPS (DGPS). This method relies on a network of fixed ground-based reference stations that continually calculate their position using GPS. These reference stations then compare their calculated position with their known geodetic position to identify any errors in the GPS signals caused by various factors such as atmospheric conditions or satellite positioning.

By broadcasting these error corrections in real-time to nearby GPS receivers, DGPS significantly enhances the accuracy of the positioning data obtained by those receivers. This process allows surveyors and users to achieve precise measurements, often improving accuracy from several meters to within a few centimeters, making it particularly useful for applications requiring high precision, such as land surveying, navigation, and construction.

The other techniques mentioned do not solely rely on simultaneous observations at a known position for corrections. For instance, Real Time Kinematic (RTK) GPS uses a base station with a known position and a rover to achieve high accuracy, but it can also employ a carrier phase measurement method that is more sophisticated than DGPS alone. Autonomous GPS works independently without reference corrections, and Static GPS involves taking measurements over a long period, which does not require simultaneous position corrections. Therefore, Differential GPS is the method that specifically fulfills