Remote sensing of the atmosphere is a fundamental and well-established method utilized across diverse fields of atmospheric research. It allows regions of the atmosphere to be studied at spatial, and temporal scales that would be impractical, or even impossible to achieve with in-situ methods. This ability is particularly useful for monitoring highly variable trace gases such as H₂O, where high-frequency measurements are essential for accurate characterization. However, ensuring the reliability of these remote-sensing instruments requires both rigorous initial calibration and validation, as well as ongoing inter-comparisons to identify biases and maintain accuracy.

This talk will be split into two distinct halves: the first being an overview of the recent Polar Night EXperiment (PONEX) campaign with a focus on the characterization of water vapour profiles from a remote-sensing, ground-based LiDAR instrument deployed during the campaign, using data from the earlier EarthCARE Commissioning Cal/Val (ECALOT) campaign. This is performed through inter-comparisons with data from a variety of both in-situ and remote sensing instruments. The second half will provide an overview of the fundamental technique and preliminary design of a remote-sensing instrument being developed to measure CO₂, H₂O, and CH₄ based on the heterodyne spectroscopy technique.