Recreational Receivers

Recreation Receivers

These receivers are generally defined as L1 Code receivers which are typically not user configurable for settings such as mask angle, PDOP, the rate at which measurements are downloaded, the logging rate, also known as the epoch interval, and signal to noise ratio SNR. As you might expect, SNR is the ratio of the received signal power to the noise floor of a GPS observation. It is typical for the antenna, receiver, and CDU to be integrated into the device in these receivers. Generally speaking, receivers that track the C/A code provide only relatively low accuracy. Most are not capable of tracking the carrier phase observable. These receivers were typically developed with basic navigation in mind. Most are designed for autonomous (stand-alone) operation to navigate, record tracks, waypoints, and routes aided by the display of onboard maps. They are sometimes categorized by the number of waypoints they can store. Waypoint is a term that grew out of military usage. It means the coordinate of an intermediate position a person, vehicle, or airplane must pass to reach a desired destination. With such a receiver, a user may call up a distance and direction from his present location to the next waypoint.

A single receiver operating without augmentation produces positions which are not relative to any ground control, local or national. In that context, it is more appropriate to discuss the precision of the results than it is to discuss accuracy. Despite the limitations, some recreational receivers have capabilities that enhance their systematic precision and achieve a quantifiable accuracy using correction signals available from earth-orbiting satellites such as the Wide Area Augmentation System, WAAS correction. In other words, some have differential capability. The Wide Area Augmentation System is a U.S. Federal Aviation Author­ity FAA and the U.S. Department of Transportation DOT system that augments GPS accuracy, availability, and integrity. The system relies on a network of ground-based reference stations at known positions that observe the GPS constellation constantly. From their data, a correction message is calculated at two master stations. This message is uploaded to satellites on geostationary orbits. The satellites broadcast the message, and WAAS-enabled receivers can collect it and use the correction provided in it. For example, it provides a correction signal for precision approach aircraft navigation. Similar systems are Europe’s European Geostationary Navigation Overlay System, EGNOS, and Japan’s Multifunction Transport Satellite, MTSAT.

Recreational grade receivers typically do not have on-board feature data collection capabilities. They also do not usually have adequate on-board storage for recording the features (coordinates and attributes) required for a mapping project. Such capabilities are not needed for their designed applications. When a recreation receiver is used to obtain an autonomous, or stand alone, position, its precision may be within a range of 5-15m, as noted in Table 4.1. Under less than optimal field conditions: tree cover and other obstructions, less than favorable GPS satellite geometry, etc., users can expect the precision of autonomous positions to lessen, sometimes substantially. The network accuracy had with real-time differential correction of 2-5m is also not always achievable due to the tendency of the Wide Area Augmentation Signal being difficult to acquire, particularly in the northern US and then only with a southern sky clear of obstruction.