基于高光谱资料对FY-1C/1D气象卫星进行交叉定标

介绍了利用AQUA卫星高光谱AIRS资料对FY-1C、FY-1D气象卫星热红外通道进行交叉定标的方法及定标结果。首先利用卫星轨道预报软件预报出AQUA与FY-1C以及AQUA与FY-1D卫星交叉点,再对交叉区域卫星资料进行像元投影和像元匹配,像元匹配包括时间、观测角度、环境均匀性等检验。以AIRS探测结果作为辐射基准,利用其观测值和FY-1卫星热红外通道光谱响应函数进行光谱匹配,最终得到FY-1卫星热红外通道的准真值并与FY-1卫星的业务产品进行比较分析。对FY-1C、FY-1D两年多卫星资料进行多次交叉比对,结果表明FY-1C通道4比AIRS观测亮温低1.3K左右,通道5低3.6K左右;而FY-1D通道4比AIRS观测亮温低0.3K左右,通道5低3.6K左右。这个准真值与FY-1观测的计数值进行再定标得到新的定标系数。     

Inter-comparison of cosmogenic in-situ He, Ne and Cl at low latitude along an altitude transect on the SE slope of Kilimanjaro volcano (3°S, Tanzania)

Because the intensity and energy spectrum of the cosmic ray flux are affected by atmospheric depth and geomagnetic-field strength, cosmogenic nuclide production rates increase considerably with altitude and to a lesser degree with latitude. The scaling methods used to account for spatial variability in production rates assume that all cosmogenic nuclides have the same altitude dependence. In this study we evaluate whether the production rates of cosmogenic ³⁶Cl, ³He and ²¹Ne change differently with altitude, which is plausible due to the different threshold energies of their production reactions. If so, nuclide-specific scaling factors would be required.Concentrations of the three cosmogenic nuclides were determined in mafic phenocrysts over an altitude transect between 1000 and 4300 m at Kilimanjaro volcano (3°S). Altitude dependence of relative production rates was assessed in two ways: by determination of concentration ratios and by calculation of apparent exposure age ratios for all nuclide pairs. The latter accounts for characteristics of ³⁶Cl that the stable nuclides ³He and ²¹Ne do not possess (radioactive decay, high sensitivity to mineral composition and significant contributions from production reactions other than spallation). All ratios overlap within error over the entire transect, and altitudinal variation in relative production rates is not therefore evident. This suggests that nuclide-specific scaling factors are not required for the studied nuclides at this low-latitude location. However, because previous studies have documented anomalous altitude-dependent variations in ³He production at mid-latitude sites, the effect of latitude on cross-calibrations should be further evaluated.We determined cosmogenic ²¹Ne/³He concentration ratios of 0.1864 ± 0.0085 in pyroxenes and 0.377 ± 0.018 in olivines, agreeing with those reported in previous studies.Despite the absence of independently determined ages for the studied lava surfaces, the consistency in the dataset should enable progress to be made in the determination of the production rates of all three nuclides as soon as the production rate of one of the nuclides has been accurately defined.To our knowledge this is the first time that ³⁶Cl has been measured in pyroxene. The Cl extraction method was validated by measuring ³⁶Cl in co-existing plagioclase phenocrysts in one of the samples.     

Toward the feldspar alternative for cosmogenic 10Be applications

The possibility of quantifying surface processes in mafic or volcanic environment using the potentialities offered by the in situ-produced cosmogenic nuclides, and more specifically by the in situ-produced ¹⁰Be, is often hampered by the rarity of quartz minerals in the available lithologies. As an alternative to overcome this difficulty, we explore in this work the possibility of relying on feldspar minerals rather that on quartz to perform in situ-produced ¹⁰Be measurements in such environments. Our strategy was to cross-calibrate the total production rate of ¹⁰Be in feldspar (P_10fsp) against the total production rate of ³He in pyroxene (P_3px) by measuring ³He and ¹⁰Be in cogenetic pyroxene (³He_px) and feldspar (¹⁰Be_fsp). The samples were collected from eight ignimbritic boulders, exposed from ca 120 to 600 ka at elevations ranging from 800 to 2500 m, along the preserved rock-avalanche deposits of the giant Caquilluco landslide (18°S, 70°W), Southern Peru. Along with data recently published by Blard et al. (2013a) at a close latitude (22°S) but higher elevation (ca. 4000 m), the samples yield a remarkably tight cluster of ³He_px - ¹⁰Be_fsp total production ratios whose weighted-mean is 35.6 ± 0.5 (1σ). The obtained weighted-mean ³He_px - ¹⁰Be_fsp total production ratio combined with the local ³He_py total production rate in the high tropical Andes published by Martin et al. (2017) allows to establish a total SLHL ¹⁰Be in situ-production rate in feldspar mineral (P_10fsp) of 3.57 ± 0.21 at.g⁻¹.yr⁻¹ (scaled for the LSD scaling scheme, the ERA40 atm model and the VDM of Lifton, 2016).Despite the large elevation range covered by the whole dataset (800–4300 m), no significant variation of the ³He_px - ¹⁰Be_fsp total production ratios in pyroxene and feldspar was evidenced. As an attempt to investigate the effect of the chemical composition of feldspar on the total ¹⁰Be production rate, major and trace element concentrations of the studied feldspar samples were analyzed. Unfortunately, giving the low compositional variability of our dataset, this issue is still pending.