GSSI Flex NX User manual

User Guide
MN73-362 Rev A
Geophysical Survey Systems Inc.
www.geophysical.com

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
Copyright © 2023 Geophysical Survey Systems, Inc.
All rights reserved
including the right of reproduction
in whole or in part in any form
Published by Geophysical Survey Systems, Inc.
40 Simon Street
Nashua, NH 03060-3075 USA
GSSI, Flex NX, Nexus, GSSI Fusion, RADAN, SIR, UtilityScan, PaveScan RDM are registered
trademarks of Geophysical Survey Systems, Inc.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
Limited Warranty, and Limitations of Liability and Restrictions
Geophysical Survey Systems, Inc. hereinafter referred to as GSSI, warrants that for a period of 24 months
from the delivery date to the original purchaser this product will be free from defects in materials and
workmanship. EXCEPT FOR THE FOREGOING LIMITED WARRANTY, GSSI DISCLAIMS ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE. GSSI's obligation is limited to repairing or replacing parts or equipment which are returned to
GSSI, transportation and insurance pre-paid, without alteration or further damage, and which in GSSI's
judgment were defective or became defective during normal use.
GSSI ASSUMES NO LIABILITY FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL
DAMAGES OR INJURIES CAUSED BY PROPER OR IMPROPER OPERATION OF ITS EQUIPMENT, WHETHER
OR NOT DEFECTIVE.
GPR UWB Compliance Notice
The FCC has granted Geophysical Survey Systems, Inc a waiver of sections 15.503(d), 15.31(c) and 15.521(d)
rules, certifying the Flex NX system and its accessories for GPR UWB transmission. This action was adopted
and released by the Chief of the Office of Engineering and Technology (OET) on 31 July 2023 and is
described in waiver DA 23-650. This waiver is subject to the following conditions:
1. The GSSI GPR device was certified by an authorized Telecommunications Certification Body. A copy
of Waiver DA 23-650 was submitted with the application for certification.
2. The Flex NX operates with stepped frequency CW modulation in 1-40 MHz steps between 30-6000
MHz
3. The Flex NX dwell time on any one frequency does not exceed 2 microseconds.
4. The dwell time during any step of the Flex NX does not exceed 0.04 percent of the device’s
minimum scan/cycle rate.
5. For certification testing, the measurement of emissions from the Flex NX was conducted with the
stepping function active for all possible frequency step sizes.
6. The Flex NX complies with all other technical and operational requirements applicable to UWB GPR
devices under Part 15, Subpart F of the Commission’s rules.
7. Operation of the Flex NX is limited to GPRs and wall imaging systems operated for purposes
associated with law enforcement, fire fighting, emergency rescue, scientific research, commercial
mining, or construction. Parties operating this equipment must be eligible for licensing under the
provisions of part 90 of § 15.509.
8. Sales of the GSSI GPR device authorized under this waiver are subject to an annual limit of 5,000
devices for each of the first two years and 10,000 devices each year thereafter.
The Flex NX is not a toy. The Flex NX cannot be used on ships or aircraft.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
FCC Class A Compliance
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1)
this device may not cause harmful interference, and (2) this device must accept any interference received,
including interference that may cause undesired operation.
Warning: Changes or modifications to this unit not expressly approved by the party responsible for
compliance could void the user’s authority to operate the equipment.
Note: This equipment has been tested and found to comply with the limits for a Class A digital device,
pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against
harmful interference when the equipment is operated in a commercial environment or residential
installation. This equipment generates, uses, and can radiate radio frequency energy and, if not installed
and used in accordance with the introduction manual, may cause harmful interference to radio
communications. However, there is no guarantee that interference will not occur in a particular installation.
Canadian Emissions Requirements
This Class A digital apparatus complies with Canadian ICES-003.
Cet appareil numerique de la classe A est conforme a la norme NMB-003 du Canada

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
Table of Contents
Limited Warranty, and Limitations of Liability and Restrictions
GPR UWB Compliance Notice
FCC Class A Compliance
Canadian Emissions Requirements
Introduction............................................................................................................................................ 1
What’s in the Box........................................................................................................................................................1
Optional Accessories.................................................................................................................................................2
System Specifications................................................................................................................................................2
Comparison of Flex NX and StructureScan Mini XT......................................................................................3
What is NEXUS™?.......................................................................................................................................................4
Flex NX and GSSI Fusion™ ......................................................................................................................................4
GPR Theory Overview ...............................................................................................................................................4
The Anatomy of a GPR Profile...........................................................................................................................5
Common GPR Uses in Concrete Scanning........................................................................................................8
Flex NX Hardware Overview............................................................................................................ 9
Handle Configurations..............................................................................................................................................9
Touchscreen Display Care and Maintenance...................................................................................................9
Battery Usage............................................................................................................................................................ 10
Powering On Flex NX and NX25 Satellite Antenna .................................................................................... 11
Pairing Satellite Antennas .................................................................................................................................... 11
Using Two GPR Antennas: Standard and Cross-Polarized....................................................................... 12
Flex NX User Interface......................................................................................................................14
Main Dashboard ...................................................................................................................................................... 14
System Settings........................................................................................................................................................ 18
Date and Time Settings .................................................................................................................................... 19
NX 25 System Settings...................................................................................................................................... 20
Health Settings ......................................................................................................................................................... 20
Health Settings: Software Update ................................................................................................................ 20
Health Settings: Updating Flex NX............................................................................................................... 21
Health Settings: Updating NX25 ................................................................................................................... 25
Health Settings: Log File Download............................................................................................................. 28
Connecting an External Viewing Device ......................................................................................................... 29
Technical Support.................................................................................................................................................... 32

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
Project Management.............................................................................................................................................. 33
Projects Portal ...................................................................................................................................................... 33
Creating New Projects....................................................................................................................................... 33
Project Profile ....................................................................................................................................................... 35
Transferring Data..................................................................................................................................................... 38
Wireless Transfer................................................................................................................................................. 40
USB Transfer.......................................................................................................................................................... 42
Collecting Data with Flex NX.........................................................................................................44
Scanning and Marking Overview....................................................................................................................... 44
Before You Scan....................................................................................................................................................... 44
Data Screen and Basic Collection...................................................................................................................... 46
Top Navigation Panel............................................................................................................................................. 48
Side Navigation........................................................................................................................................................ 49
Side Navigation: Gain Panel............................................................................................................................ 49
Side Navigation: Display Panel: Color Table Options Submenu ....................................................... 50
Side Navigation: Display Panel: Window Options Submenu.............................................................. 50
Side Navigation: Depth Panel ........................................................................................................................ 54
Target Marking......................................................................................................................................................... 58
Additional Resources........................................................................................................................59
GSSI Academy Training......................................................................................................................................... 59
Scanning and Marking Best Practices.............................................................................................................. 59
Basic Scan and Mark Techniques.................................................................................................................. 59
Data Examples .......................................................................................................................................................... 61
Wire Mesh.............................................................................................................................................................. 62
Rebar........................................................................................................................................................................ 64
Conduit ................................................................................................................................................................... 65
Pan Decking .......................................................................................................................................................... 66
Beams and Objects Strapped to the Slab.................................................................................................. 67
PVC vs. Metal Targets........................................................................................................................................ 68
Air Voids Under Concrete Slabs .................................................................................................................... 69
Multiple Reinforcement Layers...................................................................................................................... 70
PT Cables................................................................................................................................................................ 71

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 1
Introduction
Thank you for purchasing Flex NX®, the new standard in concrete scanning. This manual covers the entire
suite of product features and offers many useful tips on data collection and interpretation.
Our promise to you is to provide comprehensive training, unrivaled customer support and world-class
expertise. That’s why Flex NX includes our industry-leading two-year warranty, complimentary training,
and technical support access. For more information, visit us at www.geophysical.com.
Our team of dedicated technical trainers is ready to work with users of all experience
levels, and GSSI Academy classes are offered on an annual schedule. Check out the
GSSI Academy offerings at www.geophysical.com/gssi-academy or scan the
accompanying QR code with your smartphone.
What’s in the Box
The standard Flex NX system ships with the following:
Flex NX Controller
Part #: FGFLEX NX
Flex NX Transit Case
Part #: F-73-176
Wrist Lanyard
Part #: F-73-159
Quick Start Guide
Part #: MN73-190
Extra RAM® Mount
Part #: RAM-238U
Lithium-Ion Battery (2X)
Part #: FGNX-BAT-3 CELL
2-Bay Charger
Part #:
FGMODBC-NX

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 2
Optional Accessories
The following accessories are available for Flex NX and are sold separately:
Telescoping Pole with RAM Grip for use
with Flex NX and NX25
Part #: FGNX-POLE
NX25 Satellite Antenna
Part #: FGNX25
System Specifications
Feature
Description
Unit Type
Self-contained all-in-one GPR system
Measuring Type
Ground Penetrating Radar (GPR)
Operational Modes
Single or dual channel (stacked) LineScan, Focus Mode*
Max Depth
Flex NX and NX25**: 0-75 cm (0-30 in)
Gain Mode
Configurable automatic gain
Dielectric Settings
Configured though concrete cure, manual entry, matching, set depth
Languages
English, Spanish, Japanese, Korean, Chinese, French
Display
178 mm (7 in) LED backlit LCD touchscreen display
Storage
200 GB
Operating Temperature
-20°C to +50°C (-4°F to +122°F)
Storage Temperature
-40°C to +60°C (-40°F to +140°F)
IP Rating
IP65 (fully sealed against dust, low-pressure omnidirectional water)
Battery Performance
Flex NX up to 3.5 hours, NX25** up to 6 hours in ideal conditions
Dimensions
Flex NX: 25.3 x 13.2 x 18.9 cm (9.9 x 5.2 x 7.4 in)
NX25**: 11.2 x 11.2 x 10.4 cm (4.4 x 4.4 x 4.1 in)
Weight
Flex NX: 2.2 kg (4.9 lbs) with battery; 2.45 kg (5.3 lbs) with battery and
handle; NX25**: 0.83kg (1.8lbs) with battery
Hardware Warranty
2 years from date of purchase
*Focus Mode will be released in a future software update
**NX25 satellite antenna sold separately, or as part of the Flex NX Kit
NX25 Lithium-Ion
Battery
Part #: FGNX-BAT-2 CELL

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 3
Comparison of Flex NX and StructureScan Mini XT
If you have experience with other GSSI products, you might wonder what new features Flex NX
brings to the table. The Flex NX retains many popular features of GSSI’s previous generations of
concrete scanners, while incorporating new technology and a completely redesigned user
experience. Below is an overview of notable similarities and differences.
Operation
Mini XT
Flex NX
Locates metallic and non-metallic objects in concrete
X
X
High frequency, high resolution performance
X
X
2D scanning and data imaging
X
X
USB port
X
X
GSSI Fusion® compatible
X
X
Safety wrist strap
X
X
Quick start guide
X
X
Rugged transit case
X
X
Powered by Nexus™
X
Adjustable handle
X
Remote display
X
Wireless project transfer
X
One-pass cross polarization data collection
X
Tap-to-Connect accessories
X
Flex Vision Positioning System
X
Warranty
2 years
2 years
Subscription required
No
No
Configuration Options
Mini XT
Flex NX
Standalone or in a kit
X
X
Wired accessory antennas
Palm XT
Wireless accessory antennas
NX25
Extension pole
X
X
LineTrac®
X
Flex NX is designed to be more customizable, mobile, and convenient than our previous concrete
scanners due to software and hardware improvements. Flex NX is what you’ve come to expect
from GSSI – a cutting-edge product that is Simple, Flexible, and Trusted. Flex NX is built on GSSI’s
newly completed Nexus platform, and the first in a series of industry-defining and transformative
GPR systems.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 4
What is NEXUS™?
NEXUS is GSSI’s newest and most advanced technology platform, and it is the engine that will
drive our future industry-defining innovations. A technological triumph, the core elements of
Nexus will facilitate a profound leap forward in GPR performance, data stream integration, and
user experience. Nexus is the tangible representation of GSSI’s Simple, Flexible, and Trusted
mission, and its continual evolution will lead to vast improvements in system design, application
relevancy, and interoperability of Nexus-cored technologies. We invite you to learn more about
Nexus, and its capabilities, by contacting your GSSI sales representative.
Flex NX and GSSI Fusion™
Flex NX was designed with GSSI’s Fusion platform at the forefront. Our vision was to create a
reporting platform that seamlessly integrated with our field devices. Fusion is the culmination of
that effort. As a quick and easy reporting tool, Fusion acts as an efficient organizational system
for uploading Flex NX data, adding results and descriptions, integrating field photos, and
submitting a professional report branded with your company logo.
GSSI’s mission is to make your scanning life as painless as possible. Our ultimate goal is the
seamless interoperability of our hardware and software designs. We understand that, in most
cases, a report is a procedural bottleneck that must be submitted before you leave the jobsite. To
this end, Flex NX’s project structure mirrors GSSI Fusion’s project management environment.
Create new projects on Flex NX, create Areas of Interest and capture results and then transfer your
project to a mobile device or USB drive. Next, simply upload your projects to Fusion and your
project will be set up just like you left it. Enter notes, add field photos, and generate a report. Then
move on to your next job knowing that your polished and branded report will be digitally available
to your client.
We invite you to learn more about GSSI Fusion, and how it can streamline your project reports, by
contacting your GSSI sales representative.
GPR Theory Overview
Ground Penetrating Radar (GPR) is a geophysical method that uses radar waves to image
subsurface materials. It is commonly employed in construction, geology, archaeology, civil
engineering, and environmental studies. Nearly all GPR applications share a common goal: rapid
and non-destructive assessment of subsurface targets for mapping, avoidance, or physical
inspection. All GPR technology acts as a true remote sensing method, whereby imaging occurs
before buried targets are visually inspected. In other words, we cannot know precisely what we
are imaging until it is directly observed. However, experience with GPR will improve your
interpretation of the resulting data, and knowledge of concrete construction techniques will
provide greater insight.
GPR operates on the principles of electromagnetic wave travel and reflection. Basic GPR theory
involves an antenna transmitting short waves of electromagnetic energy into the ground,
concrete, or other material. The waves travel through different subsurface materials, partially

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 5
reflecting at boundaries with contrasting physical and chemical properties. The remaining waves
travel deeper, reflecting from other boundaries until the waves dissipate. A receiving antenna
records the reflections and plots them for display and analysis. The majority of modern
commercial GPR systems use antennas containing both transmitter and receiver.
The depth penetration and resolution of GPR depend on several factors, including the frequency
of the radar waves and the electromagnetic properties of a solid medium. Higher-frequency waves
provide better resolution but have reduced penetration depth, while lower-frequency waves have
greater penetration depth but lower resolution. Materials with high electrical resistance allow
deeper penetration, such as air, concrete, and dry sand. Materials with high electrical conductivity,
such as wet concrete and wet clay, dissipate the radar waves and vastly reduce penetration depth.
GPR measures the time elapsed between transmission and the return of reflections. The depth of
targets or layers is based on the travel time and the speed of the radar waves. As an example,
consider airplane detection using ground-based radar. The radar operator must determine the
distance to an incoming airplane. To do this, they must use a distance, speed, and time calculation.
To solve the problem, only two of the three variables are needed. The radar system records the
time elapsed between the transmitted and received signals. Radar waves travel at a constant speed
in air. The operator can then determine the distance using the time and speed values. A GPR
system works in a similar fashion, though the depth calculation is a bit more complicated. The
GPR system precisely records transmit and receive times, so we can easily constrain the time
variable. In most cases, the depth of targets is unknown. We must therefore determine the speed
of the radar waves to solve for depth. Here’s the tricky part: GPR waves travel at different speeds
depending on the material they pass through.
To calculate a precise target depth we must determine the speed of the radar waves using a
dielectric constant value. Multiple methods are available, and in order of least to greatest accuracy
these include tables of dielectric values for different materials, hyperbola matching using software,
or setting a precise target depth from physical measurements. In most cases, hyperbola matching
is the method of choice; picking a number from a table just isn’t accurate, and knowing the true
depth of a target is not common. Once the dielectric constant is determined, the system calibrates
the depth scale accordingly.
The Anatomy of a GPR Profile
GPR data are presented as vertical profiles, much like observing the side of a saw cut, displaying
depth below surface and distance traveled. As discussed above, the depth scale is only as accurate
as the current dielectric value. On the other hand, the distance scale is very precise because it is
measured with integrated distance encoders. This distance precision ensures accurate markouts,
whether collecting data in forward movement or using backup cursors when traveling in reverse.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 6
As reflections return to the receiving antenna they are plotted against travel time and assigned a
range of colors based on their phase/polarity and amplitude. The result is a single scan that is
represented by the O-Scope. Additional scans are collected as Flex NX moves forward, resulting
in a continuous GPR profile. All GPR profiles exhibit a series of flat, high amplitude bands that
appear at and around the ground surface. These reflections are the direct wave, and they are
created when GPR energy travels from transmitter to receiver before it leaves the antenna. The
center of the first positive (white) band is the position of the ground surface.
A typical GPR profile contains two categories of reflections: targets and layers. Targets are
expressed as hyperbolas representing discrete objects, such as rebar and conduit. These
hyperbolas can vary in amplitude based on the material of the object. Metallic objects produce
high amplitudes, while air-filled PVC and other synthetic materials generate weaker hyperbolas.
Target hyperbolas will widen with increased depth, and to the untrained eye these deeper targets
could be mistaken for larger objects. However, the true diameter of a target cannot be derived
from the shape of a hyperbola. Layers are continuous boundaries, like the base of a slab or an air
void under the slab, that can be tracked along a profile. Like targets, layers can vary in phase and
amplitude but their reflection characteristics are based on the nature of the overlying and
underlying materials.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 7
To an experienced GPR operator, the phase and amplitude of targets and layers reveals
additional information to enhance data interpretation. Enabling the O-Scope display will
assist with advanced interpretations. GPR energy cannot penetrate metallic targets, so a
large amount of energy is reflected back to the antenna and registers as a high amplitude
target. This is convenient for locating metal reinforcement and conduit, but solid metal
structures like pan decking are impenetrable to GPR energy. Any features of interest on
the other side of pan decking, or thick layers of metal reinforcement, will not be resolvable.
Nor can GPR image the contents of metal pipes. Additionally, metal objects display a white-
black-white pattern of stacked reflections. This pattern, along with high amplitudes,
typifies metal targets and demonstrates that the energy decreased in speed as it passed
from concrete to the metal.
In other cases, the pattern of reflections will be reversed (black-white-black). This pattern suggests
that the energy increased in speed at a material boundary, such as the air void in a PVC pipe or
an air void within or beneath a concrete slab. These reflections will often exhibit lower amplitudes
and could be masked by hyperbolas from reinforcement.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 8
Common GPR Uses in Concrete Scanning
GPR is a non-destructive method that provides insight into the condition, composition, and
structural characteristics of concrete elements. This helps in ensuring the safety, durability, and
efficient management of concrete structures. The non-destructive nature of the method makes it
a rapid, safe, and cost-effective means of identifying slab contents and potential hazards.
Concrete scanners typically use GPR to investigate concrete prior to saw cutting or core drilling.
At predetermined cutting locations the operator marks out reinforcement, conduit, and structural
elements such as beams, cables, and pan decking. This allows the cutting and coring crew to avoid
damaging important elements in the slab.
GPR is also used for non-destructive testing (NDT) and structural forensics to assess the
construction and health of existing concrete structures. In this application, inspectors employ GPR
to ensure the reinforcement in the slab and slab thickness match the planned specifications.
Commonly measured factors include rebar spacing, rebar depth in the slab, and the presence of
post-tensioned cables and other forms of reinforcement. These measurements are also carried
out when renovating older buildings, helping to verify that the concrete slabs are strong enough
to support the planned loading.
In some cases, voids form under concrete slabs due to erosion or soil compaction. Subgrade
materials can be removed by water below the slab, and compaction occurs from soil settling or
loading from above. In either case, the resulting void space poses a major risk to the integrity of
the structure. GPR is sensitive to the transition from concrete to air and can determine the areal
extent of void spaces. The slab can then be remediated, usually by injecting polyurethane foam
through numerous tiny holes drilled in the concrete. GPR can help ensure that the holes are drilled
safely, too.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 9
Flex NX Hardware Overview
Handle Configurations
The Flex NX handle is ergonomically designed to promote ease of use and maximum flexibility.
The handle is highly configurable, with a wide range of adjustment angles and built-in safeguards
to prevent screen damage. To adjust the handle, simply loosen the knob, reorient the handle, and
tighten. To remove the handle, fully loosen the knob. Use the attached RAM Mount ball to connect
an extension pole or a custom RAM solution.
Full range of horizontal rotation Vertical movement limited
to prevent display damage
Touchscreen Display Care and Maintenance
Integrated into Flex NX is a large (7.0-inch diagonal) multi-touch display. The display is not
removable and should damage occur the entire Flex NX system should be returned to an
authorized repair facility. To ensure proper care and maintenance of the Flex NX touchscreen
display, consider the following:
Clean the screen regularly. Use a soft, lint-free cloth to gently wipe the screen surface.
Avoid using abrasive materials, paper towels, or rough fabrics that may scratch the
screen. If necessary, lightly dampen the cloth with water or a screen-cleaning solution.
Turn off the display before cleaning. This allows for better visibility of smudges and
reduces the risk of accidental actions on the screen.
Avoid harsh chemicals. Harsh chemicals, solvents, or ammonia-
based cleaners can
damage the screen's protective coating. Use only mild screen-cleaning products.
Apply gentle and controlled pressure when interacting with the touchscreen. Excessive
force or tapping can lead to cracks or damage.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 10
Battery Usage
The Flex NX system and NX25 satellite antenna (sold separately) each include two Lithium-ion
batteries.
Note: the batteries are not compatible between Flex NX and NX25, but both battery styles use
the same charging station.
Flex NX Battery
To insert the battery, slide the battery door latch to the left and
open the door. Insert the battery with the battery contacts
facing upward and towards the Flex NX system. Ensure that the
battery latch is fully engaged when closed.
To eject the battery, simply slide the latch to the left and open
the door. An internal spring will partially eject the battery, and
the battery can then be removed by hand.
NX25 Battery
To insert the battery, orient the battery contacts downward.
Next, slide the battery latch lock forward and use the battery
to push up on the battery latch. The battery latch will snap
into place once the battery is fully inserted.
To eject the battery, use your index finger to slide the battery
latch lock, then insert your thumb into the front access
window and push the battery out of the latch.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 11
Powering On Flex NX and NX25 Satellite Antenna
Insert a fully charged battery, then press and hold the two power buttons to power
on Flex NX and NX25. Use this process to power down these devices; GSSI does
not recommend ejecting the battery to power down.
Pairing Satellite Antennas
Flex NX uses near-field communication (NFC) to pair with satellite antennas.
Paring a satellite antenna to Flex NX is simple. First, power on Flex NX and wait for the Main
Dashboard to appear. Next, power on NX25 and observe the red indicator light. Wait for the red
indicator light to flash blue, indicating that NX25 is ready to pair. Bring NX25 close to Flex NX and
make contact between the two NFC labels. The indicator light will transition to solid blue, then to
flashing green, and finally solid green when the two units are paired. For future scanning sessions
simply power on Flex NX, then power on NX25 and wait for the indicator light to turn solid green.
Flex NX displays NX25 data and provides complete access to NX25 configuration options and
collect mode functions. Use your satellite antenna to collect data while viewing the results on
Flex NX’s screen. Alternatively, connect a Wi-Fi enabled smartphone, tablet, or computer to mirror
the data collection screen. See the Connecting an External Viewing Device section (page 29) for
more information on screen mirroring.
Holding NX25
The NX25 satellite antenna connects to Flex NX via Wi-Fi, and GSSI highly recommends observing
safe Wi-Fi exposure habits when using this antenna. Please consult the following images, and grip
NX25 according to our recommendations.

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 12
Using Two GPR Antennas: Standard and Cross-Polarized
Flex NX contains two separate antennas with their transmitter-receiver
pairs in different orientations. The front antenna, with red lasers, is in
the standard orientation for commercial GPR systems. The rear
antenna, with green lasers, is cross-polarized. The side lasers mark the
center of each antenna, as do the front and rear lasers.
When displaying both data channels in Stacked Mode the standard
antenna (Channel 1) is the top profile and the cross-polarized antenna
(Channel 2) is the bottom profile. You’ll notice that the two channels
do not align horizontally, nor do the two backup cursors, yet targets
in both channels are aligned. Channel 2 is shifted to the right relative
to Channel 1. The offset corrects for the physical distance between the
antennas, as Channel 2 does not display data until it has passed the
starting point of Channel 1.
The two Flex NX antennas are designed to work in tandem, providing an exceptional scanning
experience employing one-pass cross-polarization. Both antennas have specific strengths. The
standard antenna is aligned perpendicular to the path of travel, as is common for most commercial
GPR systems. In this orientation it is optimized for imaging metallic targets that run perpendicular
to the direction of travel. This means that rebar, metal conduit, and other metal targets will stand
out, appearing as high amplitude (bright) hyperbolas with expansive tails.
The standard antenna orientation is the scanning workhorse, but some targets will be difficult to
image due to the nature of concrete installations. This includes PVC and other synthetic materials
that are ‘overshadowed’ by the amplitude of metallic targets. Additionally, the expansive

Geophysical Survey Systems, Inc. Flex NX®/NX25 User Guide
MN 73-362 Rev A 13
hyperbolas from wire mesh, dense rebar, and other
reinforcement often overlay and obscure deeper targets.
The cross-polarized antenna is not as sensitive to
metallic targets, though they will still appear in the
data. The main advantage is the reduction of amplitudes
from metal targets and the downplaying, or
sometimes altogether removal, of hyperbolas that
obscure deeper targets. This leads to a more refined
view of deeper slab elements, including the slab/grade
contact where air voids may be present.
By utilizing data from both standard and cross-
polarized antennas Flex NX can better discriminate
between different types of objects or materials and
improve overall data resolution and accuracy. GSSI
recommends scanning with both antennas active so
you can view a complete picture of the slab contents.
The top profile (standard orientation) shows shallow wire mesh and a possible conduit bank. In
the bottom profile (cross-polarized) the wire mesh is not visible, and the removal of hyperbolic
tails reveals more details about the conduit bank and a previously obscured target to its left.

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Flex NX User Interface
This section will familiarize new users with the Flex NX user interface. By the end of this section,
you will be able to navigate through the system, create and manage projects, and be ready to
collect data.
Main Dashboard
The Main Dashboard is the control center for Flex NX. From here, you can:
•Start a New Scan
•Access Projects
•Access System Settings
•Wirelessly connect to your personal device
•Access Technical Support
•Connect and configure NX accessory antennas
The Main Dashboard is separated into three panes: Top Navigation, System and Support, and
Recent Projects. Keep reading for a detailed description of these panes and their features.