Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar

Abstract

Abstract. Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreaker Oden during the summer of 2014. Such ship-borne Doppler measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic atmospheric boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This held true particularly within the atmospheric boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of vertical winds with a random error below 0.2 m s −1 . The comparison of lidar-measured wind and radio soundings gives a mean bias of 0.3 m s −1 (2 • ) and a mean standard deviation of 1.1 m s −1 (12 • ) for wind speed (wind direction). The agreement for wind direction degrades with height. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution shipbased wind profile measurements over the oceans.

Shipborne Wind Measurement and Motion-induced Error Correction of a Coherent Doppler Lidar over the Yellow Sea in 2014

“…The correlation coefficient R for wind direction is approximately 0.99 and almost constant with altitude up to 1.6 km. The correlation coefficient for wind speed is minimum at the lowest altitudes, and improves with height to values comparable to those for wind direction, the trends of which compare well with the results from Achtert et al (2015). An obvious feature in SD, RMSE, normalized RMSE for wind speed and direction is found at the lowest levels where the discrepancies between lidar and radiosonde data are larger than the higher levels.…”

“…In this sense, the SNR threshold value in this study is higher than the one in previous studies (Banakh and Smalikho, 2013;Achtert et al, 2015) for the same signal power spectrum. Figure 4 shows the flowchart of shipborne CDL data processing.…”

“…Whether the flow distortion around the ship is the main reason for the discrepancies in the lower part measurement or not is yet unclear. Further study, especially focused on the computational fluid dynamics (CFD) model, needs to be used to the assess the potential effects on turbulent flow and wind field analysis (Achtert et al, 2015). It is also significant for assessing turbulence fluxes exchange from sea-air interface.…”

“…Wulfmeyer et al (2005) corrected the vertical velocity using LOS velocity in zenith stare mode and horizontal wind derived from VAD mode using NOAA HRDL. Lacking real-time control of the scanning head orientation, Achtert et al (2015) placed a CDL instrument on a motion-stabilization platform to remove the effect of ship motion, and the fivepoint geometrical wind solution and the four-point sinusoidal fit method were used to obtain wind profiles, showing that motion stabilization was successful for high wind speed in open water and the resulting wave condition. Reitebuch et al (2001) presented the instrumental correction required for horizontal wind retrieval from an airborne CDL, using conical scanning pattern measurement and recalculation of the lidar mounting angle, based on the ground return speed and distance.…”

Large‐eddy simulation of a warm‐air advection episode in the summer Arctic

“…ACSE included an extensive suite of instrumentation (Tjernström et al ., ; Sotiropoulou et al ., ). The vertical atmospheric structure was measured with radiosondes, four times per day, while cloud properties were observed with a vertically pointing, motion‐stabilized W‐band Doppler cloud radar (Moran et al ., ), combined with multiple laser ceilometers and a motion‐stabilized Doppler lidar (Achtert et al ., ) to derive cloud boundaries. Two microwave radiometers provided measurements of liquid water path (LWP) and vertically integrated water vapour (IWV), as well as profiles of temperature and water vapour.…”