Thermographic (infrared/IR) imaging has been demonstrated repeatedly to reliably capture whale cues at mitigation relevant distances, including at night when visual observations are essentially futile. IR performance may however be subject to environmental conditions as well as the observed species, as a cue’s IR perceptibility requires a finite difference between cue and oceanic radiances, raising the question of to what degree this method is applicable globally. Particularly for tropical and equatorial climates, a general concern exists that warm ocean water would reduce the contrast between cue and oceanic radiance because of a lesser temperature difference between the two. Contrary to the underlying assumption that thermal contrast between cue and ocean governs the difference in radiance, our quantitative statistical analysis of 1900 cues demonstrates that the difference between oceanic radiance and both blow or body radiances is, to first order, constant, i.e. independent of the oceanic radiance, an observations also reported recently by Horton et al. (2017). Our paper explores the extent to which this correlation is subject to global ambient radiances, angular emissivity and the aspect at which the ocean background and the cue are viewed respectively, i.e., glancing with low angular emissivity for the near horizontal ocean surface versus near perpendicular with high angular emissivity for body parts and blow droplet facets. Notwithstanding the linear correlation between cue and ambient radiance, residual inter-cue variations in radiance suggest individual dependencies and thermodynamic processes modify cue radiance, aspects to be discussed with regard to their impact on the cue’s IR perceptibility.