Wide-Swath High-Resolution Immersed Grating Spectrometer for Greenhouse Gas Monitoring: Optical Design and...

Area of Science:

• Remote Sensing
• Spectroscopy
• Optical Engineering

Background:

• Spaceborne spectrometers are crucial for monitoring greenhouse gases (GHGs) globally and regionally.
• Existing grating spectrometers face limitations in balancing swath width and spatial resolution.
• Increasing demand for high-precision and high-efficiency GHG monitoring necessitates advanced spectrometer designs.

Purpose of the Study:

• To present the optical design and fabrication of an innovative immersed-grating spectrometer for GHG monitoring.
• To overcome the trade-off between swath width and spatial resolution in current spaceborne spectrometers.
• To enable wide-swath, high-spatial-resolution, and high-spectral-resolution GHG monitoring within payload constraints.

Main Methods:

• Designed an immersed-grating spectrometer with four channels covering key GHG absorption bands (0.76, 1.61, 2.06, 2.30 μm).
• Employed a prism-based simultaneous correction method to address smile and anamorphic beam compression.
• Fabricated large-sized immersed gratings using holographic lithography and ion-beam etching; aligned and tested the spectrometer.

Main Results:

• Achieved a 100 km swath width and 3 km × 3 km spatial resolution with high spectral resolution.
• Exceeded design spectral resolutions in all four channels, with values better than 0.04-0.10 nm.
• Demonstrated good imaging quality (MTF > 0.72) and minimal distortion (smile and trapezoidal distortion within one pixel).

Conclusions:

• The developed immersed-grating spectrometer offers an effective solution for wide-swath, high-resolution GHG monitoring.
• The design successfully integrates high spectral resolution with a compact optical configuration.
• This technology addresses critical constraints in detector size, SNR, and payload dimensions for effective GHG observation.