GPS data acquisition is a crucial step for many GIS projects, especially in mountainous terrain where the accuracy and reliability of the signals can be affected by various factors. In this article, you will learn about some of the key considerations for GPS data acquisition in mountainous terrain, such as:
Not all GPS receivers are created equal. Depending on your project requirements, you may need a receiver that can handle different modes, frequencies, and accuracies. For example, if you need to collect data in real time, you may want a receiver that supports RTK (real-time kinematic) or DGPS (differential GPS) corrections. If you need to collect data in remote areas, you may want a receiver that has a long battery life and a robust antenna. If you need to collect data with high precision, you may want a receiver that can use multiple GNSS (global navigation satellite system) constellations, such as GPS, GLONASS, Galileo, and BeiDou.
Using GPS data in mountainous terrain can present challenges due to the limited visibility of satellites. Tall peaks and dense tree cover can obstruct signals, leading to inaccurate location information. Multipath interference occurs when signals bounce off surfaces, creating signal delays. To mitigate these issues, consider using multi-frequency GPS devices, which are more robust in challenging environments. Additionally, augmenting GPS with other technologies like GLONASS or Galileo can improve accuracy. Using topographic maps and terrain awareness can aid in understanding signal blockages. In extreme cases, manual map and compass navigation may be necessary. Overall, while GPS is a valuable tool.
Key considerations for GPS data acquisition in mountains terrain.It depends with various aspects: 1. To Me I think it will depend on the type of the terrain, not all mountains terrain are difficult to collect data using GPS.Some mountains are sharp others are flat. 2. After knowing exactly how the mountainous terrain is looking like from there, you will be able to select which type of GPS to use (Hand Held & DGPS).For this case it is better to use DGPS as it offers data with high accuracy comparatively to Hand Held GPS. Additionally, DGPS will collect more data data than Hand Held One. 3. On the other hand, hand held GPS is easy to carry which is good for mountains terrain. Finally, renting Hand Held GPS is cheaper for use. Thank you.
When acquiring GPS data in mountainous terrain, there are several key considerations to keep in mind due to the unique challenges presented by the landscape. Overall, acquiring GPS data in mountainous terrain requires careful consideration of factors such as signal reception, interference, DOP, elevation changes, data collection strategy, and post-processing techniques. By addressing these considerations, you can obtain more accurate and reliable GPS measurements in challenging mountainous environment
You will need to look online at devices to pick your GPS hardware and software. GNSS devices are used in the field for the highest accuracy. Examples of this would be Trimble or Leica devices. These devices use many different GPS signals at once to get an extremely accurate reading of your precise location. These devices could be paired with something like a ToughPad field device or an iPad. You will also need Surveying software such as QGIS or FieldMaps by ESRI.
In my experience,mountainous places require terrain awareness and local familiarity so that one can set his/her GPS at higher altitudes,preferably without distractions to improve its accuracy and consistency.It’s also advisable to have an offline KML/KMZ map when things have gone haywire on the ground.
Before you start collecting GPS data, you should plan your survey design carefully to ensure that you cover the area of interest efficiently and effectively. You should consider factors such as the number and location of control points, the sampling interval and density, the survey method (static, stop-and-go, or kinematic), and the quality control procedures. You should also check the satellite availability and geometry for the time and place of your survey, using tools such as GPS planning software or online almanacs. You should avoid collecting data when the satellite coverage is low, the PDOP (position dilution of precision) is high, or the sky is obstructed by mountains, buildings, or vegetation.
I will recommend to use post-processing GPS such as DGPS rather than RTK (real time kinematic) as you can choose to use the correction variable later when you do a post-processing with a software for your GPS data. Planning the point and the reference point also important, you should go first for preliminary survey to plan your GPS point effectively. Also check the weather beforehand too. The need for calibration should be occured probably
When collecting GPS data in mountainous terrain, careful planning and equipment selection may not be enough to avoid challenges and errors. Multipath, which is when the GPS signal bounces off a surface before reaching the receiver, can be reduced with a choke ring antenna, avoiding reflective surfaces, and increasing the elevation mask angle. Ionospheric and tropospheric delays, which are caused by the layers of the atmosphere altering the speed and direction of the signal, can be minimized with dual-frequency receivers, atmospheric corrections, and an increased elevation mask angle. Loss of lock is when the receiver loses the connection with the satellite, creating a gap or spike in the data. To prevent this, use a stable antenna mount, avoid sudden movements or vibrations, and maintain a clear view of the sky.
Maintaining a clear view of the sky is a point that cannot be overemphasized by taking GPS readings in a mountainous terrain . You make sure you stand in a very clear view , and clear access to the sky for clearer connection to the satellite.
I have had trouble in the past where the DGPS device struggled to pick up enough satellites due to the mountainous terrain and refused to log my position. So again, it comes down to what level of quality your output requires, this was pre-smartphone but my current phone would probably have locked a position (even if the accuracy was low). If you are in the northern hemisphere, always try to face south (to pick up as many satellites as possible) and have your device raised above your head when taking readings. If taking continuous readings (e.g., a walking track rather than specific points) do not place GPS inside your rucksack!
Once you have collected the GPS data, it is essential to process and analyze it to obtain reliable outcomes. Appropriate software and methods should be used for data conversion, cleaning, correction, transformation, and analysis. For instance, you can convert raw data from the receiver format to a standard format such as RINEX (receiver independent exchange format). You can also remove any outliers from the data using techniques such as filtering or smoothing. Additionally, differential corrections or atmospheric corrections can be applied to the data to improve accuracy. Furthermore, datum transformations or projections can be used to transform the data from the receiver's coordinate system to the coordinate system of your project. Lastly, GIS software, statistical software, or visualization software can be used to analyze the data and extract useful information. In conclusion, GPS data acquisition in mountainous terrain can be difficult but worth it if you consider these key points.
An example I have seen in a project I participated which involved mapping roads on mountainous region using a high accuracy handheld GPS,Is that you need to commit alot of resources to data processing and a good base map which is updated since the data comes in very sharp and unusable and needs a lot of editing.So be ensure to consider enough time and be realistic with your client on the challenges.
QGIS is a free and open-source GIS software that can directly read in .GPX data files, the main data format exported from GPS receiver devices. Once loaded into QGIS, you can easily view, amend and manipulate the GPS data, for example, removing outliers based on some ground reference or validation you may have. GPS data will always be in WGS84 geographic coordinate reference system. There are tools to reproject to different datums depending on your study area.
The best method to ensure you have the best outcome of your project is to have a base map and three or more control points. When you carry out your survey using an RTK it's essential to use these points when picking out data. Therefore, when integrating the data you can georeference with the map and digitize your points accordingly.
1.Calibration of handheld GPS on the mountain top before taking readings or way points could optimise accuracy. It is important to select the appropriate projection and UTM zone, Nigeria has 3 zones 30, 31 and 32. 2. It is helpful to take multiple waypoints and take the average, which is referred to as the smoothing average. 3. A cross reference with an existing topographic map helps like groundtruthing. 4. The use of GPS is better under clear cloudless sky to prevent atmospheric attenuation that clock interferes with GPS clock time.
Try to make an accurate planing before, it's very important to prepare maps and tracks, don't forget weather conditions at local place. Terrain conditions, trees (canopy) maybe a hard challenge, try to consider a GPS with GNSS and a good anthena.
The first thing is a work plan on how the data is to be collected and analysed, this includes assigning different responsibilities. Set up the equipment to the right datum and as well get the latest images for the place that you are to collect data from, this comes in handy when understanding the vegetation and terrain of the place. Then comes the cleaning up of the data and this can be done in any GIS software. Realistic time frames need to be stated
GNSS survey in mountainous or urban areas need proper planning because GNSS signals obstructed by mountains in hilly area or by man-made obstacles in urban area 1. GNSS Point Site-Selection 2. Preparing Obstacle Charts for checking the GNSS observations suitable time with mission planning utility. 3. Observation Plan with redundant observations sessions. 4. Use GNSS satellites precise ephemeris data if the baseline length more than 30km. 5- Apply Least Square Adjustment to perform relative and absolute adjustments and check the point error ellipses and loop closures errors. By implementing these strategies, you can enhance the quality and reliability of GNSS observations in challenging environments like mountainous or urban areas.