Latest Developments of the ATLID Instrument: A Year from Launch of the Earthcare Mission

Abstract

ATLID (ATmospheric LIDar) is one of the active payloads of the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) spacecraft, the sixth Earth Explorer Mission of the European Space Agency (ESA) Living Planet Programme [1]. The EarthCARE mission has four instruments whose products will be used in a synergistic manner to retrieve vertical profiles of clouds and aerosols, and thereby determine characteristics of the radiative and micro-physical properties, and determine flux gradients within the atmosphere and top of atmosphere radiance. ATLID's objective is to measure vertical profiles of optically thin cloud and aerosol layers, as well as cloud boundary altitude. To achieve this, ATLID operates at an UV emission wavelength of 355.4 nm, emitting pulses of approximately 35 mJ and duration <35ns, at a repetition rate of 51 Hz, while pointing in a near nadir direction along the track of the satellite. The backscatter signal is collected by a telescope of aperture 620 mm and directed into the instrument focal plane assembly, where the atmospheric Mie and Rayleigh scattering contributions are separated and measured on separate channels. After the complete instrument integration, ATLID has had an ambient performance test campaign, followed by a mechanical, thermal-vacuum environmental and EMC qualification test campaign which included performance calibration and characterization in an approximation of on-orbit operational conditions. The analysis of the test data indicates that the instrument is compliant with expected performance goals, and will be able to meet them in orbit. The instrument has since been integrated onto the EarthCARE spacecraft, and is undergoing system level integrated checks. The EMC qualification will be completed at spacecraft level. Test data from the calibration campaign is currently being used to validate the processor software that will ingest the in-orbit data from the instrument and provide calibrated results on ground. In parallel, the flight spare of the ATLID laser has undergone a six month burn-in and lifetime test. Initial results from this test give confidence that the flight lasers have sufficient reliability to meet the designed for mission lifetime. This paper gives an overview of the design of ATLID, and presents some important results from the calibration campaign. Some preliminary data from the lifetime tests are also reported.