During a twelve day field test west of the continental shelf off the coast of Washington state, we conducted multiple environmental data collection flights in a 150 km by 150 km area. We operated a scanning lidar system optimized for ocean profiling collecting near surface atmospheric return signal, surface reflections and optical profiles to several optical depths. The along and across track spatial resolution was approximately 10 meters and the vertical resolution was approximately 0.1 meters. We also deployed ten single use temperature profiling buoys during the test. We will present comparisons of the spatial-temporal lidar data to the buoy data and other public source data, such as satellite derived k-diffuse and Argo float data. It is our expectation that the lidar data will reveal complex and changing vertical optical structures on sub-kilometer horizontal scales that are not adequately captured by other ocean sensing techniques.
During summer and fall of 2022, multiple flights were conducted with an airborne blue wavelength scanning lidar west of San Diego and in waters surrounding Iceland. Geo-registered lidar 𝑘 profiles reveal multiple ocean parameters such as mixed layer depth variations and dense plankton layers over scales of meters to kilometers. These measurements can be compared to both historical measurements of lidar 𝑘 profiles conducted with in situ instrumentation, as well as to satellite-derived measurements of ocean parameters. The main challenge of in situ oceanographic measurements is the difficulty in achieving efficient coverage of a wide area. Meanwhile, satellites cover a wide area but may not provide sufficient resolution for oceanographic studies; for example NASA’s Aqua/MODIS satellite pixel spacing resolution is on the order of 10 kilometers. The airborne lidar measurements provide larger coverage area than an in situ instrument while also providing higher resolution and greater depth penetration than a satellite measurement. This paper provides an overview of the airborne blue wavelength scanning lidar and demonstrates measurements of two ocean water properties, the average diffuse attenuation coefficient in the mixed layer and the mixed layer depth. The airborne lidar measurements of these properties show reasonable agreement with relevant satellite and in situ databases.
In this paper, we demonstrate a broadband anti-reflective (AR) coating over the mid-IR fluoride fiber endface (tip) for high power laser applications. The AR coating consists of multiple-pair Lithium fluoride (LiF) and Al2O3, and was deposited by electron beam physical vapor deposition with an iron assistant source at low temperature (<60°C). In addition, a super thin encapsulation layer (~20nm) of Al2O3 was applied over the AR coating by both traditional PVD and atomic layer deposition technology. The measurements show the coating has a reflectivity of < 1-1.5% in the range of 1.5-5.5μm. The laser induced damage threshold (LIDT) test using high power quantum cascade laser (QCL) shows the damage threshold is greater than 10 MW/cm2 with no sign of any damage on the coating. The durability and environmental tests of the AR coating with PVD coated encapsulation layer show good humidity resistance in open air and 95 RH% at 50ºC for 48 hours, no degradation of film quality and optical performance are observed. Further comparison study of ALD encapsulation layer vs pure PVD layers in more aggressive water vapor testing indicates ALD encapsulation layer has better moisture resistance.
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