Ozone Cues Mitigate Reflected Downwelling Radiance in LWIR Absorption-Based Ranging

TL;DR

This paper introduces new LWIR ranging methods that use ozone absorption features to accurately estimate distances by accounting for reflected downwelling radiance, significantly improving measurement precision.

Contribution

The paper presents two novel methods leveraging ozone absorption features for LWIR ranging, addressing the challenge of reflected radiance and enhancing accuracy.

Findings

Quad spectral method reduces error from over 100 m to 6.8 m.

Hyperspectral method further reduces error to 1.2 m.

Methods effectively estimate downwelling radiance contributions.

Abstract

Passive long-wave infrared (LWIR) absorption-based ranging relies on atmospheric absorption to estimate distances to objects from their emitted thermal radiation. First demonstrated decades ago for objects much hotter than the air and recently extended to scenes with low temperature variations, this ranging has depended on reflected radiance being negligible. Downwelling radiance is especially problematic, sometimes causing large inaccuracies. In two new ranging methods, we use characteristic features from ozone absorption to estimate the contribution of reflected downwelling radiance. The quadspectral method gives a simple closed-form range estimate from four narrowband measurements, two at a water vapor absorption line and two at an ozone absorption line. The hyperspectral method uses a broader spectral range to improve accuracy while also providing estimates of temperature, emissivity profiles, and contributions of downwelling from a collection of zenith angles. Experimental results demonstrate improved ranging accuracy, in one case reducing error from over 100 m when reflected light is not modeled to 6.8 m with the quadspectral method and 1.2 m with the hyperspectral method.