# Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning

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## Abstract

**:**

## 1. Introduction

## 2. Observation Data and Data Processing

## 3. Assessment of Observation Quality and Antenna Calibration

#### 3.1. Observation Quality

_{0}show the typical elevation dependence known from the patch and other helix antennas (Figure 4). Maximum signal levels are reached for elevation angles larger than 40 deg. Below elevation angles of 20 deg, the signal strength decreases rapidly with decreasing elevation angle. On average, GPS signal strength levels exceed those of Galileo and GLONASS signals. G5/E5 signal levels are higher than the corresponding G1/E1 signals.

#### 3.2. Integer Property of Estimated Ambiguities

#### 3.3. Antenna Phase-Center Calibration

## 4. Precise Positioning Results

#### 4.1. Dual-Frequency GPS/Galileo Precise Point Positioning

- The processing service does not accept G5 and/or Galileo observations but only the GPS (+GLONASS) traditional signal frequencies 1 and 2;
- The GPSMAP 66sr antenna does not belong to the group of antennas supported by the processing service.

- Code biases between different signals (frequencies and modulations), which are determined from the observation data of globally distributed GNSS reference station networks and are available either as differential code biases (DCBs) [17] or as pseudo-absolute code biases (observable-specific bias (OSB)) [18]. We applied the appropriate GPS DCBs produced by DLR and obtained from CDDIS [19], similar to their application described in [20].
- In the case of GPS Block IIF satellites, pronounced inter-frequency clock biases exist between G5 and G1/G2, with periods of several hours and amplitudes of up to many centimeters. They can be determined from triple-frequency GPS observations from a set of globally distributed GNSS reference stations, as described in [21]. For each of our observation days, we selected 10 globally distributed sites of the IGS (CIBG, DAV1, DGAR, KOUR, MAL2, MKEA, NKLG, NYA2, PNGM, and WTZS) and computed G1/G5—G1/G2 clock corrections, with a temporal resolution of 5 min. We applied them to the CODE GPS Block IIF clock corrections prior to the G1/G5 PPP processing.

#### 4.2. Relative Carrier-Phase Positioning with Respect to VRS

## 5. Conclusions and Outlook

## Supplementary Materials

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**Completeness of GPSMAP 66sr GNSS observations as function of elevation angle and GNSS signal.

**Figure 3.**Average number of available GPS/Galileo signals and actual GPSMAP 66sr observations per epoch at a mid-latitude site (Dresden) without any signal obstructions in mid-2021, elevation mask angle 10 deg.

**Figure 4.**Carrier-to-noise power density ration C/N

_{0}of the available GPSMAP 66sr observations as a function of elevation angle and GNSS signal.

**Figure 5.**Code noise and multipath of the GPSMAP 66sr, determined from code-minus-carrier linear combination of dual-frequency signals (RMS values).

**Figure 6.**Carrier-phase noise and multipath of the GPSMAP 66sr as determined from the observation residuals of a short baseline of two such receivers (RMS values).

**Figure 7.**Distribution of single-epoch double-difference fractional cycle ambiguities of a short, known baseline between geodetic-grade equipment and GPSMAP 66sr.

**Figure 8.**Single-difference G5/E5 residuals of a short, known baseline between geodetic-grade equipment and GPSMAP 66sr. Epoch-wise differential receiver clock errors were estimated from ambiguity-fixed observations and removed for all the observations. Residuals of those three satellites with temporary quarter- or half-cycle ambiguities are shown in colors. All other GPS/Galileo residuals are shown in gray.

**Figure 9.**GPSMAP 66sr in its holder on top of the DRB2 rotational device, which enables observations in four azimuthal orientations per minute.

**Figure 10.**Depiction of the necessary specifications with regard to antenna phase center (APC) calibration: position of the antenna reference point (ARP) and azimuthal orientation of the device toward north. The mean APCs as determined by calibration are also shown.

**Figure 11.**Results of the antenna phase-center calibration of GPSMAP 66sr for G1/E1 (

**left panel**) and G5/E5 (

**right panel**).

**Figure 12.**GPSMAP 66sr mounted on tribrach and holder for long-term observations in roof-top environment.

**Figure 13.**PPP coordinate errors (RMS values) as a function of session length for the static, roof-top observations.

**Figure 14.**Limited sky visibility at the adverse observation site due to signal obstructions and the satellite visibility gap around the north celestial pole.

**Figure 16.**PPP coordinate errors (RMS values) as a function of session length for the static observations under adverse environmental conditions.

**Figure 18.**Distribution of coordinate errors of 15 min sessions (n = 20) as 2D (north/east) and 1D (height) box-and-whisker plots depicting percentile values for 0 (minimum), 25, 50 (median), 75, and 100 (maximum): (

**a**) absolute errors with respect to station coordinates of the state survey department, (

**b**) repeatability of the 4 determinations per station.

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**MDPI and ACS Style**

Wanninger, L.; Heßelbarth, A.; Frevert, V.
Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning. *Sensors* **2022**, *22*, 1964.
https://doi.org/10.3390/s22051964

**AMA Style**

Wanninger L, Heßelbarth A, Frevert V.
Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning. *Sensors*. 2022; 22(5):1964.
https://doi.org/10.3390/s22051964

**Chicago/Turabian Style**

Wanninger, Lambert, Anja Heßelbarth, and Volker Frevert.
2022. "Garmin GPSMAP 66sr: Assessment of Its GNSS Observations and Centimeter-Accurate Positioning" *Sensors* 22, no. 5: 1964.
https://doi.org/10.3390/s22051964