Following a successful launch on May 28th, 2024, on SpaceX Falcon-9 rocket from Vandenberg, California, the long-anticipated mission is currently going through an intensive commissioning period which will extend until late 2024. At that time, the Level 1 products from the four embarked payloads will be fully calibrated, anticipated to be in-line with the performance requirements, and will become publicly available. The Level 2A, which are level 2 products derived from one sensor, as well as the two-instrument synergy Level 2B products, are also anticipated to become available few months after the Level 1. Of significant interest will be the data from the High Spectral Resolution LIDAR (HSRL), ATLID, which will allow to continue the long-term data-record for lidar derived atmospheric parameters, but will also be the first aerosol and cloud HSRL dataset publicly available, paving the way for new scientific applications.
ATLID is ESA’s second UV lidar mission, following ALADIN. It is a High Spectral Resolution Lidar, operating at 355 nm, with a depolarisation channel designed for aerosol and cloud sampling. The lidar is bistatic with separate transmission and reception chains. Its laser source generates 35 ns pulses at a repetition rate of 51 Hz, with an average pulse energy around 35 mJ, and the linearly polarised output beam is expanded so that footprint at the ground is less than 30 m and pointed 3° backwards, to minimise specular reflection from ice clouds. The receiver optical train incorporates a polarisation beam splitter that separates cross and co-polar components. The co-polar signal is further filtered by means of a high spectral resolution etalon filter to separate the “Mie” component of the signal from the ‘Rayleigh’ molecular scattering. ATLID’s vertical resolution is 103 m from the ground up to 20 km altitude and 500 m in the range 20 to 40 km altitude. Along track the sampling distance is 140 m, however consecutive pixels are summed to increase the signal to noise ratio, resulting in a spatial resolution of 280 m [2].
ATLID main level 1 products of the attenuated backscatter (ATB) profiles for the three channels - co-polar Mie channel, total cross channel and co-polar Rayleigh channel - are already being generated and the operational Level 1 processor has been conceived to constantly monitor, and correct from, the variations of each channel lidar constants as well as the various crosstalk (spectral or polarisation) coefficients. Additionally, the instrument is operated with regular spectral calibrations (tuning the emitted laser wavelength to the centre of the high spectral resolution etalon) and dark current measurements (for precise radiometric pre-calibration). Intensive testing of the instrument has also been conducted pre-launch and has demonstrated the high stability of the instrumental characteristics of the payload (laser emitted energy, detection chain radiometric noise, ...). All this ensures to generate fully calibrated Level 1 and subsequent Level 2A products in line with the performance requirements for scientific exploitation. The ATLID Level 2A products consist of an ATLID-derived feature mask, vertical profiles of extinction, backscatter and depolarisation coefficients, aerosol profiles, cloud top-height, ice-water content and effective radius, as well as target classification.
To guarantee full characterization of the scientific products, an intense validation effort is on-going since the early days of the mission, including ground-based and airborne measurement campaigns, but also modelling activities. These activities involve the cooperation of numerous international teams (with a significant contribution from US groups) involved in the cloud, aerosol and radiation scientific community. The collaborative efforts are paving the way for the exchange of good practices for algorithm development and strategies for product validation, in the frame of preparation for the upcoming AOS program and particularly its LIDAR component.
After a general presentation of EarthCARE and its associated processing chain and products, as well as the main scientific goals pursued, this presentation will then summarize the activities conducted during the commissioning period and demonstrate the early characterization of ATLID Level 1 products performances. It will then introduce the first outputs of the validation activities. Finally, an introduction to the upcoming science opportunities in the frame of EarthCARE will be given.
REFERENCES
[1] Wehr, T., Kubota, T., Tzeremes, G., Wallace, K., Nakatsuka, H., Ohno, Y., Koopman, R., Rusli, S., Kikuchi, M., Eisinger, M., Tanaka, T., Taga, M., Deghaye, P., Tomita, E., and Bernaerts, D.: The EarthCARE mission – science and system overview, Atmos. Meas. Tech., 16, 3581–3608, https://doi.org/10.5194/amt-16-3581-2023, 2023.
[2] do Carmo, J.P.; de Villele, G.; Wallace, K.; Lefebvre, A.; Ghose, K.; Kanitz, T.; Chassat, F.; Corselle, B.; Belhadj, T.; Bravetti, P. ATmospheric LIDar (ATLID): Pre-Launch Testing and Calibration of the European Space Agency Instrument That Will Measure Aerosols and Thin Clouds in the Atmosphere. Atmosphere 2021, 12, 76. https://doi.org/10.3390/atmos12010076
[3] Eisinger, M., Marnas, F., Wallace, K., Kubota, T., Tomiyama, N., Ohno, Y., Tanaka, T., Tomita, E., Wehr, T., and Bernaerts, D.: The EarthCARE mission: science data processing chain overview, Atmos. Meas. Tech., 17, 839–862, https://doi.org/10.5194/amt-17-839-2024, 2024
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