Short-range demonstrations of monocular passive ranging using O2 (X3Σg- → b1Σg+) absorption spectra

Area of Science:

• Remote Sensing
• Spectroscopy
• Atmospheric Optics

Background:

• Accurate range estimation is crucial for various applications, including defense and space exploration.
• Traditional methods may have limitations in certain environments or for dynamic targets.
• Absorption spectroscopy offers a potential passive method for remote sensing.

Purpose of the Study:

• To develop and validate a novel method for estimating range using the depth of molecular oxygen absorption bands.
• To assess the accuracy and applicability of this technique in both static and dynamic scenarios.

Main Methods:

• Observed absorption bands of molecular oxygen (O2) at 762 nm (X(v" = 0) → b(v' = 0)) and 689 nm (X(v" = 0) → b(v' = 1)).
• Estimated range by comparing measured band-average absorption with predicted curves from historical data or models.
• Validated the method using a high-resolution spectroradiometer in short-range static experiments and during a Falcon 9 rocket launch.

Main Results:

• Achieved accuracy better than 0.5% in static experiments up to 3 km.
• Demonstrated range error below 2% for the first 30 seconds of tracking a Falcon 9 rocket from an initial 13 km range.
• Observed range error remained consistent with predictions throughout the 90-second track.

Conclusions:

• The depth of molecular oxygen absorption bands provides a viable and accurate method for remote range estimation.
• This spectroscopic technique is effective for both static targets and dynamic events like rocket launches.
• The findings support the potential of this passive optical method for various remote sensing applications.