Surveying in Canopy or Urban Areas – GNSS Tips for Challenging Environments
GNSS surveying is highly accurate in open-sky environments, but things get tricky when working under dense tree canopies, near buildings, or in narrow alleys. These challenging environments can degrade signal quality, reduce satellite visibility, and result in “float” RTK status or no fix at all.
Fortunately, with the right techniques and tools, you can still collect reliable GNSS data. Let’s look at how.
🌳 Common GNSS Challenges in Difficult Areas
- 🌐 Multipath: Signals bounce off buildings, trees, or structures before reaching the antenna
- 📶 Signal Obstruction: Canopy, walls, or cliffs block direct satellite view
- 📉 Reduced Satellite Count: Limited visibility lowers accuracy and DOP (Dilution of Precision)
- ⏳ Longer Fix Times: Difficult conditions delay RTK initialization
✅ 1. Use Multi-Constellation GNSS
Modern receivers that support GPS + GLONASS + BeiDou + Galileo have better chances of locking on enough satellites, even when some are partially obstructed. Always enable all available constellations.
📡 2. Set Your Base with Clear Sky
If you’re using an RTK system, ensure the base station has unobstructed sky view for clean signal transmission. A strong base link helps compensate for poor rover visibility.
🔄 3. Use Shorter Baseline Distances
Try to keep your base station within 5–10 km of the survey area when working in dense environments. Longer baselines increase atmospheric and orbital error impact.
📱 4. Use High-Frequency NTRIP Services
Choose correction services that broadcast updates at 1 Hz or faster to help maintain fix even in partial outages. Mobile RTK apps like Lefebure, RTK4U, or Emlid Flow help manage this connection.
🛠️ 5. Adjust GNSS Settings for Stability
- 🧭 Disable unnecessary filters or smoothing
- 🛰️ Increase elevation mask to 15–20° to avoid low-signal satellites
- 📊 Monitor DOP and Fix ratio actively during logging
🧭 6. Combine with External Antennas or Total Station
In extreme cases, consider using an external GNSS antenna mounted higher (e.g., on a pole extension), or hybrid methods — such as capturing points with a total station where GNSS is unreliable.
📌 Field Tips to Improve Your Fix
- 🕒 Wait a few extra seconds per point for fix to stabilize
- 🔁 Reposition slightly to avoid blocked signals
- 🔄 Use PPK (post-processing) if RTK fails entirely
🚀 Recommended GNSS Receivers for Tough Conditions
- Leica GS18T – Excellent for canopy surveys
- Trimble R12i – Handles urban canyons very well
- CHC i93 / i90+ – Cost-effective and multi-constellation ready
- Emlid RS3 – Affordable, PPK + RTK + Tilt Compensation
💬 Final Thoughts
While GNSS under canopy or near structures isn’t ideal, modern tools and smart workflows make it possible to still achieve acceptable accuracy. Always plan ahead, monitor your data quality, and combine methods when needed.
Need help choosing the right equipment for your terrain? Let’s talk.
Next article: “Understanding UTM, WGS84, and Local Datum – A Guide for GNSS Users”