7.3 Preparation for GNSS Project Field Work
Note
Before commencing any kind of field work using GNSS (or any other kind of equipment) it is necessary to ensure that you abide by any Workplace Health and Safety requirements of your organisation.
In preparing equipment for GNSS projects, it is important that users are able to assemble, configure and operate any equipment they will be using appropriately and correctly.
Choosing a GNSS unit
The accuracy that is required for the project will generally be the most critical factor in selecting which GNSS technique you will use, and thus which equipment might be used. The list of equipment available for the various techniques is far too extensive to list here, however, a simple internet search will yield many results.
It should be noted that a number of survey grade (a GNSS unit capable of being used in GNSS surveying) receivers are integrated antenna and receiver units, however, geodetic GNSS units will usually consist of a separate antenna and receiver.
In selecting a GNSS unit that is capable of achieving the required accuracy, users should also give consideration to:
- Durability – if it is likely to be left outside for long durations, it will need to be able to withstand extreme temperatures and a variety of weather. Users in in areas of high humidity may also need to consider GNSS units that are waterproof to avoid damage to the electronics.
- Security – if the GNSS unit is likely to be in place for longer durations unattended, it is more likely to be stolen in certain locations. Considerations for site security should also include disruption by livestock – temporary electric fences might be needed.
- Weight – depending on the capacity of the user to operate or transport the GNSS unit, a more suitable unit might need to be selected, or additional people may be required to assist.
Batteries
Different GNSS units will have different batteries, and those batteries will have different discharge lengths (i.e. how long it takes a battery to run out). Users must ensure that they have sufficient batteries to last the entire duration of the field session. In some cases an external battery may need to be connected to a GNSS receiver to ensure it can observe a length of time uninterrupted. In the case of CORS, additional batteries will be needed on site to ensure that if there are any mains or solar power interruptions, the battery will need to be able to provide sufficient power to avoid any short-term outages.
Batteries also reduce in their charge over time, so a battery that lasted 6 hours when purchased, may only last for 4 hours after one or two years. This will largely depend on the type of battery and its ability to have this ‘memory’ cleared.
Data storage
The size of the storage required in a GNSS unit will depend on a number of factors:
- whether a unit is using code or phase observable
- the rate (epoch) at which data is being stored
- whether a unit is also collecting attribute data, and what attribute types are being stored
- whether other data, such as photos or scans are being collected.
Equipment settings
Most GNSS units will have default settings that represent some kind of standard configuration, however, often you will want to use a different setting better suited to the location you’re visiting, or because of the accuracy you are looking to achieve.
It is advisable to check these settings before leaving home or the office, as adjusting settings on the fly is asking for mistakes to be made if there is any confusion about setting meanings.
The main settings you should consider in any GNSS unit are discussed below.
Field reconnaissance
While the focus of this subject is GNSS, consideration of the other components of GNSS project field work are necessary to ensure that you gain a holistic understanding of field work.
Some field work might be undertaken in urban areas that are only 10 minutes’ walk or drive from your workplace, however, some others may require days of driving to reach. In each situation your organisation should have a comprehensive suite of resources that will ensure you are able to undertake the required work in a safe and efficient manner regardless of the location.
Field reconnaissance, often referred to as rece (pronounced wrecky) by surveyors, is when you visit the site you will be surveying to understand and number of factors that will include (but not be limited to): the job site, points of access, topography, vehicle access, obstructions, concerns, location of permanent survey marks and accommodation options.
The planning that can be undertaken as a result of field reconnaissance can result in time efficiencies in the field that far outweigh the cost of sending people to undertake the reconnaissance.
Use of online tools such as Google Earth and Maps have provided the opportunity for field reconnaissance to be done virtually, however, the benefits of undertaking field reconnaissance in person cannot be understated as they provide up to date information and conditions.