Two-dimensional cloud-top and surface brightness temperature with 1 Hz temporal resolution derived at flight altitude from VELOX during the HALO-(AC)³ field campaign

During the HALO-(AC)³ campaign in March-April 2022 airborne observations were performed with the High Altitude and LOng range research aircraft (HALO) covering the Fram Strait and north polar regions. The flight tracks covered open ocean areas, the marginal sea ice zone, and closed sea ice cover. Furthermore, cloud conditions were observed during air mass transformation events as marine cold air outbreaks and warm air intrusions. The thermal-infrared imager VELOX (Video airbornE Longwave Observations within siX channels) onboard HALO provided two-dimensional (2D) cloud-top or surface brightness temperature (BT) fields. The imager has a field of view of 35.5° by 28.7° (640 by 512 spatial pixels) yielding a spatial resolution of 10 m at a target distance of 10 km. The brightness temperature was measured in six spectral bands (BT1 to BT6) in the thermal-infrared wavelength range from 7.7 to 12.0 µm. Currently, BT1 and BT4 provide redundant broadband measurements for this full spectral range. The remaining four channels are narrow-band channels with central wavelengths and half-widths at 8.65 +/- 0.55 μm (BT2), 10.74 +/- 0.39 μm (BT3), 11.66 +/- 0.81 μm (BT5), and 12.00 +/- 0.50 μm (BT6). The given dataset comprises VELOX brightness temperature measurements for the four narrow-band channels and one broad-band channel. The measurements were processed and a destriping procedure, an image filtering, and a pixel correction were applied. Therefore, 2D brightness temperature fields of 635 x 507 pixels with a temporal resolution of 1 Hz are provided for 16 HALO research flights (RF) during HALO-(AC)³.