Why Not Both? The Best Emissions Monitoring Systems Don’t Choose Between Fenceline and Source-Level Detection
Summary
Fenceline perimeter systems and intrinsically safe source-mounted sensors each solve a different part of the emissions monitoring problem. Fenceline systems detect and quantify well; source-mounted sensors detect and localize well. Deploying them together — Qube at the perimeter and Qube Lite at high-risk equipment — delivers detection, localization, and quantification in a single system, at a price point that makes full-site coverage genuinely feasible.
The Three Things a Monitoring System Has to Do
Any emissions monitoring deployment ultimately needs to answer three questions:
Is there a leak?
Where is it coming from?
How much gas is escaping?
Detection, localization, and quantification. The challenge is that the physics of gas dispersion makes it difficult for any single sensor technology to do all three well.
What Fenceline Systems Do Best
Fenceline sensors, like Qube, are typically positioned 10 to 100 metres from emissions sources around the perimeter of a facility. At that distance, gas plumes have had time to spread and stabilize, which is actually an advantage: a wider, more consistent plume is easier to detect and, crucially, easier to quantify. The sensor is sampling a relatively homogeneous concentration that can be reliably translated into a mass emissions rate using atmospheric dispersion modelling.
The limitation is localization. With a sensor sitting on the fence and wind as the only transport mechanism, you can generally attribute an event to a zone or equipment group, but pinpointing the exact source within that area requires inference, not direct measurement. For many purposes, that level of resolution is sufficient. However, it can lead to frustration for operators when trying to locate the source of an alert, and often requires a handheld device such as an optical gas imaging (OGI) camera when following up on emissions.
What Source-Mounted Sensors Do Best
Intrinsically-safe sensors like Qube Lite, mounted directly on or adjacent to a piece of equipment, solve the localization problem entirely. If the sensor detects methane, you know precisely where it's coming from. There's no plume modelling, no wind dependence, no ambiguity.
The trade-off appears at quantification. Right at the source, gas concentrations are highly dynamic, fluctuating by tens to hundreds of thousands of PPM depending on pressure, wind turbulence, and leak geometry. That volatility makes it extremely difficult to derive a stable, accurate mass flow rate from concentration data alone. Source-mounted sensors excel at telling you that something is leaking and where, but quantifying how much with precision is inherently constrained by the measurement environment.
The Combined System: Better Coverage, Better Economics
When Qube and Qube Lite are deployed together, they complement each other.
Fenceline sensors handle site-level quantification and provide a continuous baseline view of aggregate facility emissions. Source-mounted sensors are deployed selectively at the highest-risk equipment, such as tanks and compression, where alertable events are most likely and where knowing the exact source matters most operationally. When a Qube Lite triggers an alert, operators know immediately which piece of equipment to inspect. When Qube detects an elevated perimeter reading, the source-level data helps confirm and localize it.
This architecture also changes the economics. Because the source-mounted sensors are covering high-risk equipment directly, you don't need the same density of fenceline sensors you would to achieve full localization from the perimeter alone. A sparser fenceline network, combined with targeted source coverage, delivers better overall performance than either approach scaled independently, and at a more attractive total cost.
The Result: Detect, Localize, and Quantify
The goal of any emissions monitoring program is a complete picture: knowing when emissions occur, where they originate, and at what rate. The combined Qube and Qube Lite system is designed specifically around that objective, pairing the quantification strength of stabilized fenceline measurements with the localization precision of at-source detection. For operators looking to build a future-proof monitoring program that meets regulatory scrutiny and operational needs without overbuilding infrastructure, the integrated approach is worth a close look.
Want to learn how Qube Technologies can help you deploy a cost-effective, comprehensive fenceline and source-level monitoring system?