Global Positioning System Receiver Antenna Research Articles

Impact of GPS receiver antenna GRAPHIC residual variations on single-frequency orbit determination of LEO satellites

Single-frequency (SF) precise orbit determination (POD) using space-borne Global Positioning System (GPS) measurements is a prerequisite for the success of many low-cost small/micro low Earth orbit (LEO) satellite missions. The first-order ionospheric effects are usually eliminated by group and phase ionospheric correction (GRAPHIC) combinations. GPS receiver antenna GRAPHIC residual variations (GRVs) are important systematic error sources in SF orbit determination. Azimuth and elevation dependent GRVs are estimated and obtained based on the GRAPHIC combination residuals in an in-flight calibration. One month of data from GRACE-A, GRACE-B, CHAMP and HY-2A satellites is used to assess the potential of receiver antenna GRVs in SF orbit determination. It is the first time to study the impact of receiver antenna GRVs on SF orbit determination for different LEO satellites, which exhibit different altitudes and data qualities. The impact of receiver antenna GRVs on SF orbit determination is significant. The use of in-flight determined receiver antenna GRVs leads to a better consistency between SF and dual-frequency POD solutions. The improvements are more obvious for GRACE-A and CHAMP satellites, whose receiver antenna GRV patterns demonstrate clear characteristics of systematic deviations. After correcting the receiver antenna GRVs, the root-mean-square of satellite laser ranging validation residuals are 3.11 cm, 2.31 cm, 2.86 cm and 5.29 cm for GRACE-A, GRACE-B, CHAMP and HY-2A satellites, respectively, which are reduced by 11.1%, 4.6%, 14.6% and 4.7%, respectively. At last, a set of a priori GDV corrections of GPS transmitter antennas are used in SF orbit determination and its effects on receiver antenna GRVs estimation and SF orbit determination are analyzed. Applying these corrections can slightly improve the SF orbit quality of GRACE-A satellite.

Assessment of Radiometer Calibration with GPS Radio Occultation for the MiRaTA CubeSat Mission.

The Microwave Radiometer Technology Acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office (ESTO). The science payload on MiRaTA consists of a tri-band microwave radiometer and Global Positioning System (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the Compact TEC (Total Electron Content) and Atmospheric GPS Sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (∼20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPS radio occultation: (1) new ultra-compact and low-power technology for multi-channel and multi-band passive microwave radiometers, (2) the application of a commercial off the shelf (COTS) GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and (3) a new approach to spaceborne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective (3), developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise. Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 K and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K.

Tests of relative vertical offsets for several types of GPS receiver antenna phase centers

The correction for antenna phase center is considered in processing Global Positioning System (GPS) data collected from a network of GPS ultra-short baselines. Compared with the leveling measurements, the GPS results show that the relative vertical offsets for the pairs of GPS receiver antenna phase centers still exist, although absolute calibration of the antenna phase center variations (PCVs) has been considered. With respect to the TPS CR.G3 antenna, the relative vertical offset for the LEI AT504 antenna is −8.4 mm, the offset for the ASH701945C_M antenna is 5.5 mm, and those for the ASH700936E_C and ASH701945B_M antennas are approximately between −2 mm and −3 mm. The relative offsets for the same type of antennas are approximately 1 mm. By correcting the absolute PCVs, the existing relative offset becomes negligible for horizontal positioning.

Phase Residual Estimations for PCVs of Spaceborne GPS Receiver Antenna and Their Impacts on Precise Orbit Determination of GRACE Satellites

In-flight phase center systematic errors of global positioning system (GPS) receiver antenna are the main restriction for improving the precision of precise orbit determination using dual-frequency GPS. Residual approach is one of the valid methods for in-flight calibration of GPS receiver antenna phase center variations (PCVs) from ground calibration. In this paper, followed by the correction model of spaceborne GPS receiver antenna phase center, ionosphere-free PCVs can be directly estimated by ionosphere-free carrier phase post-fit residuals of reduced dynamic orbit determination. By the data processing of gravity recovery and climate experiment (GRACE) satellites, the following conclusions are drawn. Firstly, the distributions of ionosphere-free carrier phase post-fit residuals from different periods have the similar systematic characteristics. Secondly, simulations show that the influence of phase residual estimations for ionosphere-free PCVs on orbit determination can reach the centimeter level. Finally, it is shown by in-flight data processing that phase residual estimations of current period could not only be used for the calibration for GPS receiver antenna phase center of foretime and current period, but also be used for the forecast of ionosphere-free PCVs in future period, and the accuracy of orbit determination can be well improved.

Monitoring dynamic and quasi-static deformations of large flexible engineering structures with GPS: Accuracy, limitations and promises

During the last few years the kinematic versions (real time kinematic (RTK) and post-processing kinematic (PPK) modes) of the satellite Global Positioning System (GPS) have been used to monitor quasi-static and dynamic deformations of large slender engineering structures. However, the accuracy of the method, the outlier level (including missed and false alarms) and its limitations have not been statistically determined. For this reason we made a large number of experiments, in which harmonic movements were simulated by a rotating GPS receiver antenna, and the recorded coordinates were compared with the real ones. The outcome of this study is that in mid-latitude regions ( φ < 5 0 ∘ ) a simple monitoring system consisting of two GPS receivers and a commercial data processing software permits a standard accuracy of up to 15 mm and 35 mm in horizontal and vertical coordinates, respectively, at 1.5% outlier level. Harmonic frequencies in the range 0.1 Hz < f < 0.5 Hz to approximately 2 Hz can also be determined. Summarizing previous research, an outcome of this study is that GPS results can be confirmed by accelerometer data and can shed light on problems such as Karman vortex vibrations, earthquake-induced oscillations and quasi-static deformations of most slender engineering structures. In addition, the GPS may prove very useful in view of recent trends for displacement deformation-based antiseismic design.

Effects of Selective Availability on GPS Positioning Accuracy

Abstract Deactivation of selective availability (SA) is expected to provide improvement in Global Positioning System (GPS) accuracy, and recent reports showed such improvements were realized immediately. However, most forestry GPS observations are made in subcanopy environments in which a GPS receiver's antenna can only receive GPS signals from a small region of the sky due to obstructions. Consequently, the satellite geometry will be poor, and position accuracy will suffer. Thus, there is a need to understand the impact of SA removal on positioning accuracy in high-PDOP subcanopy observations. This study found that it is difficult to approach the destination when GPS navigation is adversely influenced by SA accuracy degradation. When GPS positioning is performed after SA deactivation, a GPS observer can walk directly to the intended destination under thick tree canopies. Results also indicated that the horizontal accuracy is 73.3 m at the 95% probability level in the SA-degraded data set and 8.3 m in the SA-free data set. Further data analysis indicated that HDOPs (Langley 1999) recorded in the SA-on and the SA-off periods are not statistically significantly different. This suggests that a major portion of the difference in horizontal accuracies between SA-degraded and SA-free GPS observations can be attributed to difficulties in approaching the destination when SA is active. South. J. Appl. For. 26(3):140–145.

Surface reflected signals from the Global Positioning System for ionospheric measurements: Experimental results at aircraft altitudes

Several spaceborne altimeters have been built and flown, and others are being developed, to provide measurements of ocean and ice sheet topography. Until the launch of TOPEX (Ocean Topography Experiment), altimeters were single-frequency systems that were incapable of removing the effects of ionospheric delay on the radar pulse. With the current state-of-the-art in satellite altimetry, the ionosphere causes the largest single error when using single-frequency altimeters. Ionospheric models provide the only recourse short of adding a second frequency to the altimeter. Unfortunately, measurements of the ionosphere are lacking over the oceans or ice sheets where they are most needed. A possible solution to the lack of data density may result from an expanded use of the Global Positioning System (GPS). This paper discusses how the reflection of the GPS signal from the ocean can be used to extend ionospheric measurements by simply adding a GPS receiver and downward-pointing antenna to satellites carrying single-frequency altimeters. The viability of this concept hinges upon the ability to acquire and code-track the reflected signal for an extended period of time over a variety of sea states. The theory of specularly and diffusely reflected radio frequency radiation from a rough surface is reviewed. Results of experiments to demonstrate tracking of a reflected signal are presented for three aircraft flights over the Chesapeake Bay and the Eastern Shore of Virginia. The experimental hardware consisted of two off-the shelf receivers configured such that one received the GPS signal in the conventional manner using a right-hand circularly polarized (RHCP) antenna on top of the fuselage and the other could receive the reflected signal using a left-hand circularly polarized (LHCP) antenna on the bottom of the fuselage. Three tests were performed on the data to verify that the signals received in the bottom antenna were sea surface reflections: pseudorange double differences were compared against predicted geometric range double differences, characteristics of a signal reflected from a random surface were observed in the carrier to noise ratio and predicted specular points were plotted which demonstrate reflection only from wet areas. These tests indicated tracking of reflected signals for extended periods of time at altitudes of up to 5500m and sporadic signal acquisition at higher altitudes.