Spectral Measurements of Parent Soils from Globally Important Dust Aerosol Entrainment Regions

Spectral data for the paper “Spectral Characterization of Parent Soils from Globally Important Dust Aerosol Entrainment Regions” submitted to the journal of JGR: Atmospheres article number: 2022JD037666. Visible, short-wave infrared (VSWIR) and longwave infrared (LWIR) reflectance spectra as well as longwave transmission spectra presented in that paper are included in this Zenodo repository. The spectral data are stored in CSV file format in columns and the first columns are the wavelengths. <strong>VSWIR reflectance</strong>: VSWIR was measured in the wavelength range between ~ 350 and 2500 nm using Spectral Evolution (SE), model RS-5400 portable spectroradiometer with a spectral resolution of 1.5 to 3.8 nm. Soil samples were placed in an aluminum holder and the reflectance spectra collected using a contact probe, equipped with an internal halogen light source. A reflectance spectrum for a spectralon white reference panel was obtained prior to each soil measurement for calibration. All soil reflectance spectra were automatically ratioed to that of the spectralon calibration target. All spectral measurements were converted to absolute reflectance using the correction for spectralon. To obtain adequate signal to noise ratio (SNR), 60 individual scans were averaged for each final output spectrum. <strong>LWIR reflectance: </strong>LWIR reflectance was measured in the wavelength range between ~ 2.5 and 25 µm using a benchtop Nicolet 380 Fourier Transform Infrared (FTIR) spectrometer. We used a diffuse reflectance attachment that holds the sample and reference plate horizontally. Gold was used as a reference reflectance standard, because it is highly reflective at all LWIR wavelengths. Once the reference background is collected, the loaded sample holder is placed into the FTIR device to measure the sample reflectance, which is automatically ratioed to the reflectance of the gold plate. This removes the effects caused by the instrument and by atmospheric gases in the instrument path length so that features in the final spectrum are solely due to the sample. To improve the SNR, we set the numbers of scans averaged for the samples and gold reference to 100 and 200, respectively. <strong>LWIR transmission: </strong>LWIR transmission was measured in the wavelength range between ~ 2.5 and 25 µm using a benchtop Nicolet 380 Fourier Transform Infrared (FTIR) spectrometer. First, we made soil-KBr pellets using 0.5 mg of soil and 200 mg of KBr blended using a clean mortar and pestle for 2 to 3 minutes to ensure uniform dispersion of mineral particles in the matrix. Pellet production was performed with the means of an evacuable KBr Die Kit and a CrushIR Digital Hydraulic Press from PIKE Technologies (Madison, WI, USA). The mixture was first transferred to the Die Kit which was then pressed under vacuum for about 4 to 5 minutes at a pressure of ~ 10 t cm^-2, forming a hard disk 13 mm in diameter. Due to the hygroscopic nature of KBr, we pulled a vacuum on the pellet die for approximately 3 to 4 minutes prior to compression, and we immediately placed the pellets in a desiccant box, and then measured transmission within one or two hours of pellet creation. The pellet was attached to a self-adhesive sampling card and placed into the transmission holder. The resulting transmission spectrum for the sample is recorded with the dust-KBr mixture measurement being ratioed to that for an empty chamber, or blank reference. To avoid contamination of transmission spectra with ambient gases, the instrument was initially purged with dry air for at least 5 minutes, prior to each transmission collection. To increase the quality of the spectra and improve the SNR, the numbers of scans averaged were 200 for the blank reference and 100 for the samples.本Zenodo仓库收录了投稿至《地球物理学研究杂志：大气（JGR: Atmospheres）》、文章编号为2022JD037666的论文《全球重要沙尘气溶胶起尘区域母质土壤光谱表征》中的光谱数据，包含该论文中提及的可见-短波红外（Visible, short-wave infrared, VSWIR）反射光谱、长波红外（Longwave infrared, LWIR）反射光谱以及长波红外透射光谱。光谱数据以CSV文件格式按列存储，第一列为波长数值。 **可见-短波红外反射率**：可见-短波红外反射光谱的测量波长范围约为350~2500 nm，使用Spectral Evolution（SE）型号RS-5400便携式光谱辐射计完成采集，该仪器的光谱分辨率为1.5~3.8 nm。将土壤样品置于铝制样品架中，通过配备内置卤钨光源的接触式探头采集反射光谱。每次土壤样品测量前，均先采集Spectralon白色参考板的反射光谱以完成校准，所有土壤反射光谱会自动与该Spectralon校准靶的光谱做比值运算，随后结合Spectralon校正系数将所有光谱转换为绝对反射率。为获得足够高的信噪比（Signal to Noise Ratio, SNR），每张最终输出光谱均对60次独立扫描结果进行平均。 **长波红外反射率**：长波红外反射光谱的测量波长范围约为2.5~25 µm，使用台式Nicolet 380傅里叶变换红外（Fourier Transform Infrared, FTIR）光谱仪采集。实验采用可水平放置样品与参考板的漫反射附件，以金作为反射率参考标准，因其在所有长波红外波段均具备高反射性。先采集参考背景光谱，随后将装有样品的样品架放入FTIR仪器中测量样品反射率，测量结果会自动与金板的反射光谱做比值运算，以此消除仪器本身以及仪器光程内大气气体带来的干扰，使最终光谱中的特征仅来源于样品本身。为提升信噪比，将样品与金参考的平均扫描次数分别设置为100次与200次。 **长波红外透射率**：长波红外透射光谱的测量波长范围约为2.5~25 µm，同样使用台式Nicolet 380傅里叶变换红外（FTIR）光谱仪采集。实验步骤如下：首先制备土壤-KBr压片：称取0.5 mg土壤样品与200 mg溴化钾（KBr），使用清洁的研钵和研杵研磨2~3分钟，确保矿物颗粒在基质中均匀分散。压片制备采用PIKE Technologies（美国威斯康星州麦迪逊市）生产的可抽真空KBr压片模具套件与CrushIR数字液压压力机。将混合粉末转移至压片模具中，在约10 t·cm⁻²的压力下真空加压4~5分钟，制成直径13 mm的硬质压片。由于溴化钾具有吸湿性，我们在加压前先对压片模具抽真空约3~4分钟，且在压片完成后立即将其置于干燥箱中，并在压片制备后的1~2小时内完成透射光谱测量。将压片粘贴至自粘采样卡后放入透射样品架，样品的透射光谱通过将土壤-KBr混合样品的测量结果与空腔（空白参考）的光谱做比值运算得到。为避免环境气体对透射光谱的污染，每次透射光谱采集前，均先用干燥空气吹扫仪器至少5分钟。为提升光谱质量与信噪比，将空白参考与样品的平均扫描次数分别设置为200次与100次。