Airborne observatory for high-resolution land surface temperature and spectral emissivity

The Land surface temperature and emissivity Airborne Observatory System (LAOS) provides land surface temperature (LST) and spectral land surface emissivity (LSE) at very high spatial resolutions (0.5–4 m) and flexible (e.g., intraday) acquisition times. LAOS enables: (i) to map spectral variations in LSE—an inherent property of land surface materials—and (ii) to analyse spatial and temporal variations in LST in relation to land surface processes. Here, we present the scientific rationale for developing the system, the components of the hardware and the processing chain, and retrieval and validation results from an agricultural case study. The LAOS hardware consists of a HyperCam-LW (Telops Inc.), a Fourier transformed infrared spectrometer that operates in the long-wave infrared (7.7–11.5 µm) and an associated airborne platform. The processing chain includes radiometric calibration, generation of ortho -photo mosaics, noise removal, atmospheric correction (AC) and temperature and emissivity separation (TES). Key innovations with respect to previous airborne hyperspectral TIR studies are an improved noise filtering step and a recalibrated minimum emissivity—spectral contrast relationship derived from an extended set of ECOSTRESS spectral library spectra . For demonstrating LAOS’ capacities, an extensive survey campaign was conducted over the Burana Irrigation Consortium area near Modena, Italy, on 13–15 July 2022. Images were acquired at 1- and 4-meter resolution during three times of the day. Raw image tiles were processed to LST and LSE mosaics and compared with ground measurements. Validation was performed over agricultural surfaces – wheat stubble, melon, and water –providing a more surface-type-diverse assessment than previous more urban-focused studies. The LST mosaics show good agreement with the in-situ temperatures across all three surface types (within-class R 2 = 0.52–0.86, RMSE = 2.0–3.2 K, global R 2 = 0.96). LSE maps reveal crisp changes at field boundaries and appear relatively constant over time (i.e., both during a day and across multiple days). Airborne LSE spectra show mostly reasonable agreement with ground measurements and reproduce the overall spectral shape. Spectral emissivity remains largely stable both diurnally and across days (average variability ∼ 1.1 %), indicating consistent retrieval performance at field scale. The results demonstrate that LAOS produces LST and LSE maps with accuracies consistent with previous hyperspectral TIR studies, showcasing its potential to address pressing questions in various fields, including agriculture (e.g., irrigation), forestry (e.g., stress detection), defence (e.g., target detection), and urban studies (e.g., urban heat islands). As a high spatial resolution airborne TIR imager, LAOS can also serve as a demonstrator for upcoming satellite missions, such as LSTM (Land Surface Temperature Monitoring, ESA), TRISHNA (Thermal Infrared Satellite for High-Resolution Applications, CNES & ISRO), and Eagle-TIR (Explorer for Artemis Geology Lunar and Earth, NASA).