Field-based measurement technologies are a subset of "real-time measurement technologies," so the terms are not exactly interchangeable. The term commonly refers to measurement techniques that can be deployed on-site during the course of a characterization or remediation program to generate analytical data. A number of terms are equivalent, such as field analytics, field analytical methods (sometimes abbreviated as "FAMs"), on-site analysis, and others. They all convey the idea that analysis is being performed at or near the location where the environmental samples were collected, as opposed to samples being shipped off to a distant laboratory. In contrast, a distant laboratory may provide data results rapidly enough to support in-field decision-making, and so qualify as "real-time measurements" under the Triad, but would not be considered field-based. "Field-based" denotes a level of hardware robustness and mobility that is different from what one would expect with standard fixed-laboratory measurement systems. Field-based methods have advanced tremendously over the past 5 to 10 years in response to evolving capabilities in lasers, electronics, molecular biology, computerization, microfabrication, and other fields.

Field-based measurement technologies cover a wide range of technical options, including systems capable of in situ measurements, systems that perform ex situ measurements on sampled media in the field, and systems that can be deployed in an on-site, mobile laboratory. In contrast to the rather rudimentary capabilities of ten years ago, field analytical methods now provide analytical performance that spans a wide range of quality and utility. Some field methods provide the non-specific, qualitative, or semi-quantitative analyses (often collectively called "screening analyses") traditionally associated with field analysis. However, a growing number of field techniques are able to provide the quantitative, analyte-specific analyses typically associated with standard fixed-laboratory techniques. With the appropriate technology and QA/QC protocols, some field-based systems can provide data that are of the same or even better quality than traditional fixed-laboratory analyses.

The cost of field-based measurement technologies varies: field data are often much cheaper per data point than fixed-laboratory counterparts, but occasionally per-sample cost may be more expensive than standard fixed-laboratory analyses. In that case, the utility of the field method derives from its ability to save even greater resources because real-time decision-making improves the efficiency of expensive field crews and their equipment. Balancing costs against benefits for sampling and analytical options is an integral part of systematic planning, such as Step 7 of the DQO process.