Retrieval of the real part of the refractive index of smoke particles from Sun/sky measurements during SCAR‐B
Retrieval of the real part of the refractive index of smoke particles from Sun/sky measurements during SCAR‐B
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从 SCAR-B 期间的太阳/天空测量中检索烟雾颗粒折射率的实部
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
P. Artaxo
中科院分区：
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作者：
M. Yamasoe;Y. Kaufman;O. Dubovik;L. Remer;B. Holben;P. Artaxo
一种方法被用来使用光谱天空辐射的角度依赖的地面测量来恢复整个垂直柱中环境气溶胶颗粒的折射率的实部。该方法利用巴西Cuiaba的AERONET(气溶胶机器人网络)辐射计在1995年的SCAR-B(烟雾、云和辐射--巴西)实验期间测量的太阳/天空光谱数据，应用于烟雾气溶胶粒子。折射率是由太阳上的测量结果与Mie理论的计算结果进行比较而得到的。首先由散射角小于40°的天空辐射得到气溶胶的尺寸分布，然后由20°-100°的天空辐射得到折射率。模拟和灵敏度研究表明，预期误差为±0.03。将该方法应用于以塞拉多植被燃烧产生的烟雾为主的Cuiaba地区，得到438、670、870和1020 nm波长的折射率实部平均值分别为1.53±0.04、1.55±0.04、1.59±0.02和1.58±0.01。虽然我们没有对结果进行独立验证，但我们测试了水蒸气对折射率的影响。在巴西测得的低湿度系数和高相对湿度的缺乏表明水蒸气的影响很小。事实上，正如预期的那样，在折射率的反演值和总的可降水量之间没有明显的相关性。在美国东部(这里没有报告)高湿度和高增湿因子的气溶胶中的应用表明，随着总可降水量的增加，折射率显著降低，从而使人们对该方法产生信心。
A method is used to retrieve the real part of the refractive index of ambient aerosol particles in the entire vertical column using ground-based measurements of the angular dependence of the spectral sky radiance. The method is applied to smoke aerosol particles using spectral Sun/sky data measured by the AERONET (Aerosol Robotic Network) radiometers in Cuiaba, Brazil, during the SCAR-B (Smoke, Clouds, and Radiation-Brazil) experiment in 1995. The refractive index is retrieved from comparison between measurements taken in the solar almucantar and calculations using Mie theory. First the aerosol size distribution is derived from sky radiance at scattering angles less then 40°, then the refractive index is derived from sky radiances for angles of 20°–100°. Simulations and sensitivity studies are presented showing that the expected error is ±0.03, Application of the method to the Cuiaba region, which is dominated by smoke from cerrado vegetation burning, resulted in a mean value for the real part of the index of refraction of 1.53±0.04, 1.55±0.04, 1.59±0.02, and 1.58±0.01, respectively, for wavelengths of 438, 670, 870, and 1020 nm. Though we do not have independent verification of the results, we tested the effect of water vapor on the refractive index. The low humidification factors measured in Brazil and the lack of high relative humidities suggested a small effect of water vapor. In fact, as expected, a nonsignificant correlation was observed between the retrieved values of refractive index and total precipitable water vapor. Application to aerosol in the eastern United States (not reported here), with high humidity and high humidification factors, did show a strong reduction of the refractive index with increase of the total precipitable water vapor, thus generating confidence in the methodology.