Accuracy, iPhone SOS, updated videos and Andy's top tips

How accurate is an Outdoor GPS unit/ GPS watch and what settings can you adjust to make it better and also what other factors affect accuracy?

New videos in the GPS Training online resource – what new videos have we added and a special discount code

Apple iPhone 14 SOS facility, initial thoughts?

Andy’s top tips

   

How accurate is an Outdoor GPS unit/ GPS watch and what settings can you adjust to make it better and also what other factors effect accuracy.

Currently in Orbit

GPS – 31 with 24 operational 95% of the time – Dual Frequency L1 & L5

In March 2021, about 52% of GPS satellites had L5. By 2023, we expect about 71%

GLONASS – 23 Operational – Single Frequency L1

GALILEO – 30 with 24 operational – Dual Frequency E1 & E5

Accuracy

We tend to find using  GPS & Galileo we achieve approx.. 10ft (3m) Glonass similar

We have seen with GPS & Galileo / WASS & EGNOS on with a high sensitive antenna GPS Device e.g. GPSMap 65,66,86 Montana 700 Series accuracy down to approx. 8ft (2.5m)

We tend to find with Multi Band + GNSS  using a GPSMap65s or 66sr unit accuracy approx. – 7ft (2M) we have seen this down as low as 5ft (1.5m)

Things that affect accuracy - How are you holding the device, view of sky, tall buildings cliffs etc.

A handheld Device needs to lock onto 4 x Satellites locked to determine both your location and GPS height data.

 

Etrex 10,22x,32x, Touch 25 & 35 use GPS or GPS & Glonass + Waas / Egnoss

Oregon 700– use GPS or GPS & Glonass + Waas / Egnoss

GPSMap66s uses GPS or GPS & Glonass or GPS & Galileo + Wass / Egnoss

GPSMap66i uses GPS or GPS & Galileo + Wass Egnoss

Montana 700 uses GPS or GPS & Glonass or GPS & Galileo + Wass / Egnoss

Montana 700i / 750i uses GPS or GPS & Galileo + Wass / Egnoss

GPSMap65s & 66sr – GPS or Multi GNSS or Multi GNSS + Multi Band

Multi GNSS Picks up GPS, GLONASS & Galileo

Multi GNSS + Multi Band (Dual Frequency) - GPS, GLONASS & Galileo L1 (e1)  & GPS & Galileo L5 (e5)

When the 65 or 66sr receives multi-band from a satellite, it can use those multiple signals to do quality analysis and correction, reducing the error introduced by bouncing signals (multi-path error) and the earth's atmosphere.

What Advantages Do Multi-Band Devices Have Over Other Models?

More consistent tracklogs and improved positioning when using the device in challenging environments (e.g. around tall buildings in urban canyons as well as tree cover).

Can achieve accuracy within about +/- 2 meters or 6 feet under ideal conditions versus the +/- 3 meters or 10 feet accuracy of other models.

Detect (and reject) reflected satellite signals better than a single frequency receiver which improves accuracy.

Better equipped to account for and correct errors that can be introduced by atmospheric effects (e.g. ionosphere errors).

 

WAAS - Wide Area Augmentation System

WAAS consists of multiple ground reference stations positioned across the U.S. that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through 1 of 2 geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

Who benefits from WAAS?

Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult...