Great questions, Marshall! In the past many roof thermographers used mid-wave sensing (2-5 micron) cameras such as the Inframetric ThermoCam or the Agema 550 (these were, at the time, known as short-wave sensing cameras; same wave band but the name has changed!). In fact they tend to give better imagery on many single-ply membranes such as the two you mention and EPDM.
The issue appears to be related to the spectral reflectivity of these materials (more reflective in long-wave and less so in mid-wave) and the cold (clear) sky they are/are not reflecting. I still know many roofers who prefer older systems to newer, long-wave systems. The problem is exacerbated by the fact that (10 we often look at roofs at a fairly shallow angle which increases reflection and (2) any low spots on the roof tend to collect dirt and become less reflective compared to high spots—all of which can add to the confusing images.
The attached images were taken using long-wave systems on white PVC (left), clearly showing an area of wet insulation and on EPDM (right) clearly showing a reflection and fasteners. In my experience—and in talking to those who have even more than I— today's long-wave systems can work fine even if they may not be as effective as mid-wave systems.
Interestingly, the problem is often NOT the membrane but rather the fact that the insulation used with these single-ply membranes is relatively non-absorbent foam. The moisture is there but, especially in newer roofs, not as easily traced because it is not so readily absorbed. As the insulation ages, it become more absorbent and the patterns are easier to understand.
Interestingly, the National Roof Contractors' Association (NRCA) strongly recommends that the top most layer of insulation in all single-ply roofs be a layer that can absorb moisture (typically condensation) and can provide some cushioning.
The bottom line: There are no portable mid-wave systems available today except used ones and long-wave systems are better than no system! My suggestion is to persist with the amazing technology (long-wave) that we have available to us today!
Thermally Yours,
John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820