IR Remote Sensor Combines Detection, Imaging

A new dual-band remote sensor splits the infrared radiation given off by an object into a long-wave portion for detection and into a mid-wave portion for spectral analysis to simultaneously detect and image an IR source.

All things with a temperature greater than absolute zero emit thermal IR energy. Human vision, most sensitive to the shorter-wavelength visible light, can detect or differentiate between the longer-wavelength thermal IR signatures given off both by living beings and inanimate objects. Mechanical detection of IR radiation has been possible since Samuel Pierpont Langley invented the bolometer in 1880, but devices that can also recognize and identify an IR source after detection have proved more challenging to develop.

The novel infrared remote sensing system built by researchers at two Chinese universities combines long-wave and short-wave infrared bands to simultaneously detect and image an IR source. Images courtesy of Tianxu Zhang/Zheng Fang.

Conventional remote sensing systems share a single sensor for both imaging and spectral data processing. The new instrument designed by researchers at Xiamen University and at Huazhong University of Science and Technology has separate sensors for each task and uses a dichroic beamsplitter to divide the IR signal from an object into two components, a long-wave IR (LWIR) beam and a mid-wave IR (MWIR) beam.

"The LWIR beam goes to the imaging sensor and the MWIR to the spectrum recognition sensor," said Tianxu Zhang, a physicist at Huazhong University of Science and Technology and corresponding author of a paper on the research. "This allows us to simultaneously obtain high spatial resolution, frame rate and spectrum resolution, resulting in higher sensitivity for measuring the IR spectrum than currently available combined IR imaging and spectral-analysis devices."

The researchers increased the capability of their instrument by mounting it on a 2-D rotating stage. "Once we locate a target of interest, especially a moving one, the stage lets us keep the object in view and sample its IR," Zhang said. "This gives us the ability to define an object's IR spectral curve very precisely and better use the data to distinguish it from another IR radiating source."

The experiment (tracking an airplane) using the novel infrared remote sensing system developed by researchers at two Chinese universities.

In their experiment, they used the dual-band IR remote sensing system to observe the spectral curves of the sun and airplanes in flight from distances up to 6 km (4 miles). "We learned that spectral curves of aerial moving targets are different when measured from different directions," Zhang said. "So the more data collecting multiple curves for an object, the more distinctive its IR signature."

They plan to use their remote sensing system to build a database of such highly defined signatures. "We want to add the spectra of as many objects as possible to our data set, thereby increasing the accuracy and reliability with which we can identify objects," Zhang said.

A paper on the work, "Dual-band infrared remote sensing system with combined LWIR imaging and MWIR spectral analysis" appears in Review of Scientific Instruments (http://dx.doi.org/10.1063/1.4818668) .