Influence of humidity on the aerosol scattering coefficient and its effect on the upwelling radiance during ACE-2
Influence of humidity on the aerosol scattering coefficient and its effect on the upwelling radiance during ACE-2
复制标题
DOI：
10.3402/tellusb.v52i2.16657
复制
发表时间：
2000-01
期刊：
影响因子：
--
通讯作者：
S. Gassó;D. Hegg;D. Covert;Don R. Collins;K. Noone;E. Öström;B. Schmid;P. Russell;J. Livingston-J.
中科院分区：
文献类型：
--
作者：
S. Gassó;D. Hegg;D. Covert;Don R. Collins;K. Noone;E. Öström;B. Schmid;P. Russell;J. Livingston-J.
在1997年6月和7月进行的第二次气溶胶特性实验（ACE-2）期间，在加那利群岛周围区域，在不同相对湿度（RH）下测量了海洋上空的气溶胶散射系数（σsp），作为高度的函数。这些数据是由华盛顿大学安装在派力肯研究飞机上的被动湿度计（UWPH）收集的。同时，在17次飞行中测量了颗粒尺寸分布、吸收系数和气溶胶光学厚度。利用σsp作为相对湿度的函数的参数化来评估气溶胶水合作用对上升流辐射的影响（归一化为太阳常数和天顶角的余弦）。在对应于EOS-AM“Terra”（探测器、中分辨率成像光谱仪和MISR）的可见光和近红外波段的波长处模拟了大气辐射信号的顶部。UWPH在2个RH下测量了σsp，一个低于环境条件，另一个高于环境条件。通过这2个测量值的插值获得环境σsp。数据按3种气溶胶进行分层：撒哈拉尘埃、清洁海洋（海洋边界层背景）和污染海洋气溶胶（即，2-或从欧洲平流输送的1天前的污染气溶胶）。σsp对RH依赖性的经验关系式，定义为σsp（RH）=k。（1-RH/100）-γ，与从数据中导出的吸湿指数γ一起使用。3种气溶胶类型的γ值分别为：γ（灰尘）=0.23±0.05，γ（清洁海洋）= 0.69±0.06，γ（污染海洋）=0.57±0.06。根据测得的γ s，利用上述方程导出了不同吸湿性的气溶胶模型。卫星模拟信号代码6S被用来计算对应于这些气溶胶模型在几个环境湿度上升流辐射。对于发射前传感器的估计精度和仪器的假定观测几何形状，模拟表明，MISR测量的反射率的光谱和角度依赖性不足以区分具有干成分、γ和环境RH值的各种不同组合的气溶胶模型。在可见光波段，中分辨率成像分光仪也观察到类似的现象。然而，2100 nm波段的中分辨率成像光谱仪似乎能够区分至少相同的气溶胶模型与不同的气溶胶吸湿性给定的中分辨率成像光谱仪校准误差的要求。这一结果表明，气溶胶吸湿率的MODIS反演的可能性。
Aerosol scattering coefficients (σsp) have been measured over the ocean at different relative humidities (RH) as a function of altitude in the region surrounding the Canary Islands during the Second Aerosol Characterization Experiment (ACE-2) in June and July 1997. The data were collected by the University of Washington passive humidigraph (UWPH) mounted on the Pelican research aircraft. Concurrently, particle size distributions, absorption coefficients and aerosol optical depth were measured throughout 17 flights. A parameterization of σsp as a function of RH was utilized to assess the impact of aerosol hydration on the upwelling radiance (normalized to the solar constant and cosine of zenith angle). The top of the atmosphere radiance signal was simulated at wavelengths corresponding to visible and near-infrared bands of the EOS-AM )“Terra” (detectors, MODIS and MISR. The UWPH measured σsp at 2 RHs, one below and the other above ambient conditions. Ambient σsp was obtained by interpolation of these 2 measurements. The data were stratified in terms of 3 types of aerosols: Saharan dust, clean marine (marine boundary layer background) and polluted marine aerosols (i.e., 2- or 1-day old polluted aerosols advected from Europe). An empirical relation for the dependence of σsp on RH, defined by σsp(RH)=k. (1−RH/100)−γ, was used with the hygroscopic exponent γ derived from the data. The following γ values were obtained for the 3 aerosol types: γ(dust)=0.23±0.05, γ(clean marine)= 0.69±0.06 and γ(polluted marine)=0.57±0.06. Based on the measured γ's, the above equation was utilized to derive aerosol models with different hygroscopicities. The satellite simulation signal code 6S was used to compute the upwelling radiance corresponding to each of those aerosol models at several ambient humidities. For the pre-launch estimated precision of the sensors and the assumed viewing geometry of the instrument, the simulations suggest that the spectral and angular dependence of the reflectance measured by MISR is not sufficient to distinguish aerosol models with various different combinations of values for dry composition, γ and ambient RH. A similar behavior is observed for MODIS at visible wavelengths. However, the 2100 nm band of MODIS appears to be able to differentiate between at least same aerosol models with different aerosol hygroscopicity given the MODIS calibration error requirements. This result suggests the possibility of retrieval of aerosol hygroscopicity by MODIS.