![]() However, no effort has been made to validate the wind speed estimates from OCO-2 until now. These reflectances are primarily a function of illumination, viewing geometry, and wind speed. It measures reflected sunlight in three near-infrared bands and uses a Cox–Munk ( Cox and Munk, 1954) sea surface slope model to estimate reflectance when over water surfaces. The Orbiting Carbon Observatory-2 (OCO-2 Crisp et al., 2008) is one such instrument. In addition to missions specifically designed to measure wind speed, many spaceborne sensors that measure reflected sunlight in the visible or near-infrared must have some way of accounting for reflection off of specular surfaces such as the ocean. The spatial resolution of these passive sensors typically ranges from 20–35 km. They all measure at microwave frequencies from 6 to 37 GHz at both vertical and horizontal polarizations, allowing for the removal of atmospheric attenuation effects. Examples of passive sensors include the Special Sensor Microwave Imager (SSM/I Hollinger et al., 1990 Wentz, 1997), the Special Sensor Microwave Imager Sounder (SSMIS), the Tropical Rainfall Mission Microwave Imager (TMI Wentz, 2015), the Global Precipitation Mission (GMI Draper et al., 2015 Wentz and Draper, 2016), and the Advanced Microwave Scanning Radiometers (AMSR-E and AMSR2 Imaoka et al., 2010). The characteristics of this radiation depend on wind-induced effects on surface roughness and the production of white caps ( Bourassa et al., 2010), so typically a radiative transfer model is used to estimate wind speed from these emission characteristics (e.g., Wentz, 1997 Meissner and Wentz, 2012). Wind speed (but not direction) can also be estimated from measurements of radiation obtained by passive microwave instruments that operate at a variety of frequencies. This wind speed measurement technique is limited in that it does not work over land or ice surfaces.Īctive instruments, including scatterometers (e.g., SeaWinds – Spencer et al., 2000 ASCAT – Figa-Saldaña et al., 2002 RapidScat – Durden and Perkovic-Martin, 2017), altimeters (e.g., SEASAT – Born et al., 1979 SARAL-AltiKa – Lillibridge et al., 2014), and synthetic aperture radars (e.g., RADARSAT-1 – Parashar et al., 1993 ALOS PALSAR – Rosenqvist et al., 2007) estimate wind speed and sometimes direction by sending electromagnetic pulses to the surface and then detecting and characterizing the backscattered radiation. Ocean surfaces respond quickly to the movement of the air above them, and thus the surface roughness pattern is a function of both wind speed and wind direction. Technically, these satellites are sensitive to the surface roughness. Both active and passive sensors are used to estimate wind speeds, and these measurements are typically made in the microwave frequency range in order to penetrate through clouds and most precipitation. ![]() These measurements have proven extremely valuable in improving weather and climate models while advancing our understanding of oceanic and atmospheric physics. Surface wind speed has been measured by satellites going back nearly half a century. Although OCO-2 is restricted to clear-sky measurements, potential benefits of its higher spatial resolution relative to microwave instruments include the study of coastal wind processes, which may be able to inform certain economic sectors. −0.22 m s −1, an RMSD of 0.75 m s −1, and a correlation coefficient of 0.94. Sensors, with OCO-2 having a small mean bias against AMSR2 of Using this, we find excellent agreement between the two Modifications are tested, with the most successful being a single-bandĬox–Munk-only model. Several different OCO-2 retrieval algorithm ![]() In the international Afternoon Constellation (A-Train), allowing for a large number ofĬo-located observations. This work, retrieved wind speeds from OCO-2 glint measurements are validatedĪgainst the Advanced Microwave Scanning Radiometer-2 (AMSR2). ![]() Orbiting Carbon Observatory-2 (OCO-2) are also sensitive to the wind speed. Surfaces, measurements of reflected sunlight in the near-infrared made by the ![]() Sensors are traditionally used to detect surface wind speed over water Satellite measurements of surface wind speed over the ocean inform a wide ![]()
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