Groundtech GR-4 Series 3D Ground Scanners

Groundtech GR-4 Series Overview

The Groundtech GR-4 and GR-4 DUAL share the same scanner: the MFS-2 dual gradiometer sensor (plus or minus 2000 µT), a 480 MHz processor, and a built-in 240 x 280 pixel color screen at 850 cd/m². Groundtech rates the 3D scan on both at up to 15 meters (49 ft) and says the results show magnetic metals such as iron and steel differently from non-magnetic metals such as gold, silver and copper, along with voids such as tunnels and rooms. Both run on a rechargeable 7.2 V 3.2 Ah lithium-ion battery rated up to 10 hours in 3D scanning, charge over USB Type-C with a 25 W adapter, save 10 scans on the unit and carry Groundtech's 2-year warranty. Pair either one over Bluetooth 5 (LE) with the G-Portal app for Android and iOS when you want to study scans in 3D and 4D.

Groundtech GR-4 vs GR-4 DUAL: Which Should You Buy?

The GR-4 is a scanner only, with three modes: 3D Ground Scan, Live Scan and Pinpointer. The GR-4 DUAL adds a 404 Hz pulse-induction metal detector with the PiD35 search coil, plus Detector Fast Scan and Detector Advanced Scan, for five modes in all. Groundtech says the detector separates ferrous from non-ferrous metal and rates it up to 3 meters (10 ft). The DUAL weighs 1,364 g (3.0 lb) against 760 g (1.7 lb) for the GR-4.

Our recommendation: buy the plain GR-4 if you already own a good detector and pinpointer for recovery, because the scanner is the part you are paying for. Buy the GR-4 DUAL if you want one unit that scans deep and then works the top layers of the same spot, with no second machine to carry. Groundtech does not say a GR-4 can be converted later, so decide on the detector first.

Groundtech GR-4, Best For:

• Detectorists who already own a detector and want to add a deep 3D scan
• Reading scans on the unit instead of a phone in your hand
• Walking larger grids with the lighter of the two GR-4 units

Groundtech GR-4 DUAL, Best For:

• Scanning a site and checking the marked spot with one machine
• Telling ferrous from non-ferrous targets in the upper soil before you dig

Key Features in the Field

The built-in screen is the main difference between a GR-4 Series unit and the phone-based Groundtech GR-3 Series. Settings, the active mode and the scan graphics show on the device. Live Scan gives immediate feedback as you walk, and we like it for a first look at a site, but a quick live response does not replace a properly run 3D grid scan when you need a detailed analysis. The Pinpointer function then fixes the target's position on the surface. We treat the screen as the field tool and G-Portal as the desk tool: scan and mark on site, then review the saved scans and a survey report before you dig. The body folds, the grip angle adjusts and the sensor module is removable, which Groundtech highlights for transport.

Gradiometer Scan and Pulse Induction: Two Different Readings

On a GR-4 DUAL, the 3D scan and the pulse-induction detector answer different questions. The gradiometer scan responds to disturbance in the ground's magnetic field, which is how it maps larger objects and voids deep down. The pulse-induction detector transmits into the ground and responds to metal near the coil, which is why it suits checking a marked spot before and during the dig. We like that the two technologies give you different information, but combining them does not guarantee an accurate identification of the target. Our metal detector technologies explained page covers how pulse induction works.

Where the GR-4 Series Works Best and Its Limits

A GR-4 Series unit is at home on a defined site you have permission to survey: an old farmstead, a suspected cache location or ground where you expect a void. Groundtech's rated scan depth is a maximum for large objects and voids, and small objects read much shallower. Groundtech publishes no waterproof rating for either unit, so keep it out of the rain, and it rates both for use from minus 10 to 60 °C (14 to 140 °F). Our page on how deep metal detectors go explains why rated depths are ceilings rather than typical results.

GR-4 Series, GR-3 Series or A2 Series

The Groundtech GR-3 Series is the lower-cost route if a phone as the display does not bother you. The GR-3 PLUS carries the same rated depth as the GR-4 in a one-piece wand.

The Groundtech A2 Series is the step up, with more rated depth, a pulse-induction detector with three coils and a headset, and on the A2 GEO a geo-electric system for groundwater and deep cavities. If the GR-4 DUAL is already on your list and you expect to work deeper sites, compare it against the A2 in the table below before you decide.

What Comes in the Box and What Fits

Groundtech's standard contents for the GR-4 are the main unit with its built-in screen, the MFS-2 dual sensor module, a charging adapter, a carrying bag and the user manual; the GR-4 DUAL box adds its detector coil, and the DUAL ships in two boxes. A pinpointer still earns its place for the last few inches of the hole; see Groundtech pinpointers.

Groundtech 3D Scanner Comparison

All six Groundtech scanners use a plus or minus 2000 µT gradiometer sensor and differ in rated depth, extra instruments, display and battery.

Our Groundtech buyer's guide compares the full Groundtech range. Scan only where you have permission; see metal detecting laws and ethics.

Why Buy the Groundtech GR-4 Series from Serious Detecting?

• Free Shipping on Orders Over $99: Your Groundtech GR-4 or GR-4 DUAL ships at no extra cost across the continental US.
• Authorized Groundtech Dealer: Showroom in Ypsilanti, Michigan, full 2-year manufacturer warranty and product registration support.
• Help Before and After You Buy: Our staff answer setup, coil and GR-4 Series questions by phone or email.