Mirage of sun glitter reflections from lakes in Brittany

In a variation on the above theme, we looked for other sources of bright sun reflection and found a pair of adjacent lakes in the hilly Monts d'Arrée region along the spine of Brittany, Lac Drennec and Lac Brennilis, at 155m (500ft) and 225m (740ft) respectively. The latter seemed to be divided by a promontory in a position that might even help explain a "dark band". The larger lake, 3.9km long, would subtend something approaching 1.0° of arc from the 225km (123nmi) distance of ORTAC, in the right range for the angular size of UAP#1.

Fig.28. Lines of sight to Lakes Drennec and Brenillis, Brittany, possible candidates for miraged sun glint reflections (Google Earth image).
Fig.28. Lines of sight to Lakes Drennec and Brenillis, Brittany, possible candidates for miraged sun glint    reflections (Google Earth image).

Problems here begin with the fact that specular reflection from favourably oriented wave surfaces would again be required. (The bearing of Lac Brennilis from the Trislander, 220°, would be up to ~7° away from the sun azimuth.) Significant ocean swells are obviously not a factor in this case, so the local wind friction is the only available generator of wave slopes. Interpolating between the nearest height readings of the Brest radiosonde (noon ascent), winds were 222°, 12 knots. The direction is favourable. As was the case with the Plougasnou sea bay scenario we are not sure that a ~10 knot breeze is sufficient to generate enough 20° capillary wavelet slopes. Being a small lake there is no adverse ocean swell orientation, but at the same time the wind fetch is very short and the lake is sheltered by hills on the windward side.

A more serious problem is that the terrain in front of the lakes is also elevated. Lac Brennilis at 225m has a ridge of terrain rising to >300m within 3nmi on the line of sight, and its little sister, Lac Drennec,at 155m, has 200m terrain within 2-3nmi. For the more interesting Lac Brennilis this represents about a 0.8° obstruction, and even assuming a flat earth the elevation angle to the Trislander at ORTAC (3460ft above datum) would be only about 0.25deg. The ray bending required to refract light from the lake surface over this terrain seemed extreme, and the situation would be worse when the plane is down near 2000ft towards the end of the sighting.

We explored this by plotting elevation angles over a digital elevation model of the Monts d'Arree topography. We found that reflections from Brenillis below 0.6° - 0.8° would indeed be masked by the hills and that the situation was even worse for Lac Drennec, which would be entirely masked below 1.1°. With such steep reflection angles, the reflected rays would reach the coast 60km away at more than 3000' ASL in a standard atmosphere, and yet observers descending to 2000ft a further 135km (74nmi) away were able to see the UAPs. The requirement is for a very strong and deep optical duct rising to perhaps 600m (~2000ft) or more, contributing a ray curvature several times the earth-radius trapping value of 33"/km in a short distance, in order for the rays to be refracted earthward before being released by the duct at a point still far enough from the Trislander to be observed (as variously described; Appendix B) "against the sea","coming from the sea", "against the sea and the land [Guernsey]" or at a depression angle approaching "2 degrees" below the horizontal n1 Email to Martin Shough from Andrew Young, San Diego U., 01.09.07: The local elevation of the ray as it exits the duct can be no more than a few minutes of arc. In order for this ray to reach the observer at a depression angle of 2°, the observer's astronomical horizon must make an angle of about 2° with the horizon at the point where the ray leaves the duct. In other words the observer has to be nearly 2° of a great circle on Earth away from the end of the duct, or about 120nmi. The total distance from the initial sighting point NNE of ORTAC to the lake is about 132nmi, which would allow only ~12nmi (22km) path length both for coupling into the duct and for propagation within the duct. A refraction of 2° in this distance implies ray bending >10 times as severe as an optical trap and a temperature gradient proportionately steep. However the situation is worse than this, because the estimated elevation angle to the UAPs (appearing nearby and co-altitudinal with the Trislander"s FL40) was initially near 0° and the depression angle only increased towards the estimated 2° ("against the sea and the land", Capt Bowyer) just before descent, when the aircraft was within ~113nmi of the lake. (Immediately after the start of descent Kate Russell confirmed the impression that UAP#1 appeared to be "coming from the sea). Clearly there is now no distance (actually, a negative distance) available for propagation within the duct. We can try to resolve this by reducing the required depression angle. If we halve the angle to 1° below the horizon we still have only 53nmi (97km) available for coupling into, and for propagation within, the duct. An 11.6°C/100m trapping gradient produces about 53arcmin refraction in that total distance. But we only get the benefit of that refraction if light rays near 0° elevation are available from the source in the first place. In this case most of the first 53arcmin of refraction is cancelled out because the minimum angle of reflection for masked rays coming from the lake is already greater than about +40arcmin. So in practice we have only in the order of -10arcmin depression in the first 53nmi (6"/km) for a trapping gradient, which means that even a visual depression angle as small as ~0.5 degree (¼ of that estimated) requires about twice the refractivity due to a 33"/km duct and thus well over 20°C/100m of temperature inversion, which is completely unsupportable..

So the lake hypothesis requires a temperature gradient several times the +11.6°C/100m optical trapping gradient. But meteorological evidence, including the Meteo-France numerical simulation of the temperature profile over the Breton coast, shows no sign of any elevated inversion at all, and there appears to be no mechanism that could produce such an extremely strong trapping layer (Section 5). The only inversion for which there is meteorological evidence is a marginally-ducting surface layer capped at 200m above the sea, whose boundary is 100m below the level of the hills that mask Lac Brenillis from the observers, and indeed below the level of the lake itself. No light rays from the lake surface could even couple into this duct.

To summarise some problems with this theory: Very unrealistic temperature gradients are required for which there is no evidence; capillary slopes favourable for specular reflection on the lake are far from certain; no mechanism exists for the duplication of laterally separated images with the same internal detail; no explanation exists of the lateral rotation of the two LOSs relative to one another; the change in angular size of the distant lake during the sighting would be fractional and could not approach the factor 2.6 observed; and the object observed from the Jetstream on a near-reciprocal sightline would be an unexplained coincidence.

Plausibility (0-5): 1