Guide to a Successful GPR Survey

Before You Turn On the Equipment, Read This

The quality of a GPR study is defined before you arrive at the field. A poorly planned survey produces data that even the best software can't save. A well-planned survey — even with basic equipment — generates information that supports confident decision-making.

This guide is based on over 20 years of experience processing GPR data from around the world. We've seen it all: from impeccable surveys done by engineers with no prior geophysics experience, to unrecoverable data produced by equipment costing hundreds of thousands of dollars. The difference is almost never the equipment — it's the planning.

Step 1: Define Your Objective Clearly

Before touching the GPR equipment, answer these questions:

• What am I looking for? — Pipes, cavities, stratigraphy, water table, rebar in concrete, buried objects…
• At what depth is the target expected? — This defines the antenna and configuration.
• What type of ground is at the site? — Sand, clay, rock, fill, pavement…
• How large is the target? — This defines line spacing.
• Is there prior information? — As-built drawings, geotechnical reports, aerial photos, local knowledge…

Step 2: Select the Right Antenna

GPR antenna frequency defines the balance between penetration depth and resolution. Higher frequency = more resolution but less depth. Lower frequency = more depth but less resolution. This table summarizes the most common options:

*Actual depth depends enormously on soil type. In dry sand you may achieve double; in wet clay, half or less.

General rule: If you have access to more than one antenna, use the highest frequency that reaches your target depth. More resolution is always better, as long as you reach the depth you need.

Step 3: Design Your Line Layout

Line layout design is probably the single most important factor for survey success. Three fundamental rules:

Rule 1: Lines perpendicular to the target

If you're looking for a pipe running north-south, your lines should run east-west (perpendicular). A line parallel to the pipe can pass right over it without detecting it. If you don't know the target orientation, survey lines in two perpendicular directions (grid).

Rule 2: Line spacing

Maximum line spacing should be smaller than the target you're looking for. References:

• Buried utilities (pipes, cables): 0.5 – 1.0 m between lines
• Cavities / voids: 1.0 – 2.0 m between lines
• Archaeological features: 0.25 – 0.5 m between lines
• Geological studies / stratigraphy: 2 – 5 m between lines

Rule 3: Line extensions

Always extend your lines beyond the area of interest — minimum 2-3 meters on each end. This provides context and greatly facilitates interpretation.

Area: 20 x 30 meter parking lot
Target: Locate pipes (~30 cm diameter)
Antenna: 400 MHz

East-West lines: 31 lines, 1 m spacing
  → L01-EW to L31-EW (South to North)
North-South lines: 21 lines, 1 m spacing
  → L01-NS to L21-NS (West to East)
Extension: Each line extends 3 m beyond the area

Total: 52 lines (~2,700 linear meters)
      

Step 4: Configure the Equipment Correctly

Configuration depends on your specific equipment, but these are the universal parameters to consider:

Time Window (Range)

The time window defines the maximum depth the GPR records. Set it to see at least 1.5 times your target depth. If you're looking for something at 2 meters, configure the window to reach 3 meters. This gives you context below the target.

Trace Interval (Station Spacing)

How often the equipment takes a "snapshot" of the subsurface along the line. For most applications, an interval of 2-5 cm is adequate. For fine detail (rebar in concrete), use 1 cm. For geological studies, up to 10-25 cm.

Survey Speed

Maintain a constant, appropriate speed so the equipment can acquire data at the configured interval. In wheel/odometer mode, speed adjusts automatically. In time mode, speed directly affects the actual interval.

Step 5: Execute the Survey

Ground contact

For ground-coupled antennas, surface contact is critical. The GPR antenna must slide along the ground without lifting. On irregular surfaces (cobblestone, unpaved), advance more slowly and carefully.

Direction consistency

Record the direction of each line. The most practical convention is to define a "zero point" for each line and always advance in the same direction. This is essential for generating 3D models (time-slices).

Markers and references

Use your equipment's marker/fiducial function to flag known reference points along each line — corners, edges, visible pipes, posts, etc. This allows correlating GPR data with reality.

Common field mistakes

• Lifting the antenna off the ground: Produces noise and false reflections. Maintain constant contact.
• Irregular speed: Distorts trace spacing. Maintain constant speed.
• Not recording obstacles: If you have to divert around an obstacle (post, bench, car), note it. It will appear as an anomaly in the data.
• Forgetting the sketch: Without a sketch, data loses spatial context. Draw the lines on a simple site plan.
• Not checking data in the field: Periodically review radargrams on screen. If the signal looks dead (no reflections), there may be a configuration or contact problem.

Step 6: Document Everything (This Is What Makes the Difference)

Field documentation is what separates a professional GPR study from an amateur one. Without context, data is lines and colors — with context, it's information.

Minimum required documentation

• Site sketch — With numbered lines, start/end points, north arrow, and references (buildings, streets, posts).
• Site photos — Panoramic and detail shots of the surface, equipment in operation, and any visible references.
• Surface type — Asphalt, concrete, dirt, grass, cobblestone, etc.
• Ground conditions — Dry, moist, saturated. Has it rained recently?
• Equipment settings — Antenna used, time window, trace interval, acquisition mode.
• File naming — Ensure you can match each file to each line on the sketch.

Ideal documentation (added value)

• GPS coordinates of line start/end points, or continuous GPS track.
• Existing drawings — As-builts, topographic plans, previous studies.
• Geological/geotechnical information — Expected soil type, known water table depth, site history.
• Specific objective by zone — If different areas have different objectives, document it.

Project: Central Plaza Parking Lot
Date: January 15, 2026
Equipment: GSSI SIR-4000 + 400 MHz Antenna
Operator: Eng. Martinez

Settings:
  Time window: 50 ns (~2.5 m)
  Trace interval: 0.02 m (every 2 cm)
  Mode: Wheel (odometer)
  GPS: Integrated (on)

Surface: Asphalt in good condition (~10 cm)
Soil: Sand-gravel (per 2019 borehole)
Conditions: Dry, sunny, 82°F
Last rain: 5 days ago

Lines: L01-EW to L31-EW (S→N, 1m spacing)
       L01-NS to L21-NS (W→E, 1m spacing)

Observations:
  - L12-EW: Manhole cover visible at meter 8.5
  - L15-EW to L18-EW: Wet zone, meters 12-15
  - L05-NS: Detour around parked vehicle, meters 10-12
      

File Naming: Organize Your Data

Clear file naming makes processing easier and avoids confusion. We recommend the following format:

[Project]_[Zone]_[Line]_[Direction].[extension]

Examples:
  CentralPlaza_ParkingLot_L01_EW.dzt
  CentralPlaza_ParkingLot_L02_EW.dzt
  CentralPlaza_ParkingLot_L01_NS.dzt
  WaterPipe_MorelosStreet_L01_NE.dt1
      

If your equipment doesn't allow long filenames, use a short code and keep a correspondence table:

FILE001.DZT → Central Plaza, L01-EW (S→N, starting at SW corner)
FILE002.DZT → Central Plaza, L02-EW (S→N, 1m north of L01)
FILE003.DZT → Central Plaza, L01-NS (W→E, starting at SW corner)