GPS and GNSS technology has revolutionized the world around us, cutting into so many facets of life that we don’t even know anymore. One of them is land surveying, as it has made it immensely easier to help professional surveyors do their jobs with greater ease and maximum precision. GPS/GNSS tools help surveyors provide accurate data and produce results much faster compared to the older times.
One of the most essential tools needed to make this happen are GNSS antennas. Their function is to provide an interface between GNSS receivers and satellites, enabling precise PNT services while capturing satellite signals in multiple frequency bands. Today we want to explain how a GNSS antenna works and how they help make land surveyors’ lives much easier.
GNSS Antenna vs GPS Antenna: What’s the Difference?
To get the basics out of the way, many people do get confused between the two terms, GPS and GNSS. GNSS is an abbreviation of Global Navigation Satellite System, which is actually the umbrella term used for all satellite (satnav) navigational systems in the world. The satnav systems included are Galileo, GLONASS, Beidou, and, of course, GPS.
GPS (Global Positioning System) represents only a single component of GNSS. It was originally developed for the use of the US military and was developed by the United States Department of Defense. It was made public in 1994 and already has 32 medium Earth orbit satellites, representing the most used GNSS in the world.
GPS vs GNSS Antenna: Which is Better?
GNSS has three segments, the space segment, the control segment, and the user segment. The space segment includes the satellite which sends signals back to Earth. The control segment are actually the stations located on Earth that help monitor and correct time as well as orbit parameters of satellites. The user segment, the most important one for us, is the device that we are using to receive and process the signals sent to us by the GNSS satellite.
The devices included can range from smartphones to advanced GNSS receivers. So picking the right type of receiver can help you obtain better results. But you have to understand that GPS receivers only have access to GPS. On the other hand, GNSS receivers offer access to multiple satellite systems.
GNSS receivers have the advantage of offering you uninterrupted signals. If one system fails, or the line of sight is interrupted, you can always switch to a different one as a backup. This could be crucial when you are working in the field and are trying to get the exact measurements needed.
Therefore, you should know that not all GPS receivers are compatible with GNSS. But all GNSS receivers are compatible with GPS. Keep this in mind when getting the proper land surveying equipment for your next job.
GNSS Antenna Characteristics
Getting the exact antenna GNSS for the job you are working on can help to get better accuracy and improve the efficiency of your entire system. Thus, knowing and understanding the GNSS antenna parameters is crucial when you are trying to make the right pick.
GNSS signals can actually be very weak, so to get the best possible results, you have to get a high-performing antenna and receiver. However, something that a lot of users underestimate is the optimal integration of the antenna. Poor integration can lead to bad results, which you definitely don’t want when you are doing a very complex and precise survey.
To make this happen, you have to think about the following characteristics of the antenna you are purchasing.
- Antenna gain
- Group delay variation
- Axial ratio
- Phase center offset (PCO)
- Phase center variation (PCV)
How Can You Find the Best GNSS Antenna for Land Surveying Tasks?
When picking the best survey-grade GPS antenna for your needs, you have to understand that a one-glove-fits-all solution does not really exist. Technology still hasn’t gotten to where we want it to be, so there is always going to be some kind of tradeoff, whether it is between availability, accuracy, reliability, etc. So the first thing that you need to know is which part is the most relevant to you, allowing you to start from there.
GNSS Antenna Types
GPS used in surveying can be of a lot of help, but you need to pick the type of antenna that you are going to be using based on the type of survey you are conducting. For instance, geodetic antennas are created for permanent installations, making them more accurate.
On the other hand, there are portable survey antennas which are way more rugged and easier to set up. They are much more appropriate for various types of fieldwork. But are a little less accurate.
Your decision should be made based on the purpose of the TGPS antenna. You need to take into account the environment you are working in, the precision level required, and the GNSS signals you are planning to capture.
Key Features
There are three main features that surveyors need to consider when picking a GNSS antenna - gain pattern, axial ratio, and noise figure. The gain patterns is something that should be uniform for all, as it helps to minimize the loss of a signal at low elevation angles.
A low axial ratio should also indicate a better overall quality of signal reception. This is particularly important when dealing with multi-path interference. Finally, a low-noise figure is desirable as it helps the antenna pick up weaker signals without being overwhelmed by background noise.
Durability Needs
A surveying GPS antenna needs to be durable enough to withstand all the harsh conditions and types of environments where you are planning to conduct surveys. You need to take into account extreme temperatures, moisture, physical impacts, etc. This is why you absolutely need to look for antennas that have high ingress protection (IP) ratings.
This indicates that they are resistant to solids and liquids. Also, a robust GPS antenna design will ensure consistent performance over a longer period of time. It will eliminate the need for constant replacements and help protect the integrity of the data you are collecting.
Compatibility Check
You absolutely need to make sure that your existing surveying equipment is compatible with the GNSS antenna that you are purchasing. Not to mention the compatibility of your current software with the GPS antenna app. You have to think about the antenna interfacing with your data collectors, processing software, and receivers.
Checking the compatibility in advance will not only prevent any potential integration issues, it also prevents compromising data accuracy. Not to mention that you will be cutting on costs which could incur with you trying to obtain some added appropriate equipment. You can resolve this situation by picking up an antenna that supports multiple constellations and frequencies.
Budget Balance
Spending wisely is the best formula when buying a good GNSS antenna. You can get a Trimble GPS antenna with ease, but you have to take into account how much you are willing to spend, as well as the purpose and the type of job you are doing.
If accuracy is of utmost importance, spending more is justified. If providing the most accurate data possible is paramount to you, spending a few extra bucks is okay. But you can still get quality results with lower-priced products. You just have to check all the specifications and see if they match your needs.
User Reviews
Don’t underestimate the power of reading some user reviews. They hold much more insight than you may think. The valuable experience that other customers had may help you understand how well the antenna you are planning on purchasing could work for you. Everyone surveying professional can read the technical specifications, but getting first-hand experience from somebody that already used the device is much more useful.
Accuracy
For most, accuracy acts as the top priority when getting a GPS/GNSS receiver. However, the actual level of accuracy will depend on the application you are planning to use it for. For instance, surveying and mapping require centimeter-level perfection, while activities like hiking can be done with meter-level accuracy.
GNSS satellites are very precise, but there are still several factors that can reduce their precision. For example, the clock of a satellite may drift by a few nanoseconds, which could result in huge errors when it comes to precision. Orbit errors may also occur, the multipath effect, and ionospheric and tropospheric delays.
Availability
Depending on the application, but in some situations surveyors require accurate positioning even in areas with blocked or weaker satellite signals. The best way to avoid such problems is a multi-frequency, multi-constellation receiver. But you also have to think of avoiding the multipath effect.
Alternatively, you can also get INS (Inertial Navigation System) devices that integrate with your GNSS ones. INS is a type of technology that can compute position based on acceleration and angular velocity measurements. Combining GNSS and INS will ensure continual availability of navigation and position during surveys.
First Fix Time
The fix time is the time needed for a receiver to provide a position. Depending on the type of job you are doing, you may require a fast fix time, but there are others that don’t really need it. There are some types of GNSS devices that have a fix time of 11 seconds, and those may be the ones you are looking for if time is of the essence for you.
However, there are GNSS receivers that have multiple simultaneous channels, which also helps to reduce the time needed to establish an initial fix. Unfortunately, devices with a fast fix time also tend to increase the probability of a wrong position.
Other Factors to Consider When Choosing a GNSS Receiver
While we mentioned the main factors that need to be considered, there are still several more that are a bit less important. Either way, they deserve a mention.
- User-friendly interface: Consider how easy it will be for you to use the device.
- Memory and storage: Very important if you are planning to store large amounts of data.
- Connectivity: Be sure to consider the most ideal ways for you to transfer the gathered data.
- Size and weight: The size and weight will determine the portability of the device.
- Operating time: If you are planning to spend long hours in the field, a device with a longer battery life will suffice.
- Future proof: Get a device that is capable of using new signals and constellations once available.
GNSS Antenna FAQs
For a few more pieces of helpful information about GNSS antennas, check out the answers below.
Do surveyors use GPS?
Yes, surveyors frequently use GPS technology for various tasks in modern land surveying.
What is a GPS antenna used for?
A GPS antenna is an essential component in any GPS system. Designed to receive satellite signals from the Global Positioning System (GPS) satellites orbiting the Earth.
What does a GPS antenna look like?
A GPS antenna can come in various shapes and sizes depending on its application. But most share some common design features.
What does a GPS antenna do?
A GPS antenna's primary function is to receive signals from GPS satellites and transmit those signals to a GPS receiver. The receiver then processes the signals to determine the precise location, time, and velocity of the GPS user.
What is a GNSS antenna?
A GNSS antenna is a special antenna that can receive signals from multiple satellite navigation systems, not just GPS. In addition to GPS, GNSS antennas can receive signals from other global satellite constellations. These include GLONASS (Russia), Galileo (Europe), BeiDou (China), QZSS (Japan), or IRNSS/NavIC (India).
How does GNSS surveying work?
GNSS surveying is a method of determining precise positions on the Earth by using signals from multiple satellite constellations. It works similarly to GPS surveying but uses multiple satellite systems to improve accuracy, availability, and reliability.
