Observing the earth radiation budget from satellites: Past,present, and a look to the future

Satellite measurements of the radiative exchange between the planet Earth and space have been the objective of many experiments since the beginning of the space age in the late 1950's. The on-going mission of the Earth Radiation Budget (ERB) experiments has been and will be to consider flight hardware, data handling and scientific analysis methods in a single design strategy. Research and development on observational data has produced an analysis model of errors associated with ERB measurement systems on polar satellites. Results show that the variability of reflected solar radiation from changing meteorology dominates measurement uncertainties. As an application, model calculations demonstrate that measurement requirements for the verification of climate models may be satisfied with observations from one polar satellite, provided we have information on diurnal variations of the radiation budget from the ERBE mission.     

The earth radiation budget experiment: Early validation results

The Earth Radiation Budget Experiment (ERBE) consists of radiometers on a dedicated spacecraft in a 57° inclination orbit, which has a precessional period of 2 months, and on two NOAA operational meteorological spacecraft in near polar orbits. The radiometers include scanning narrow field-of-view (FOV) and nadir-looking wide and medium FOV radiometers covering the ranges 0.2 to 5 μm and 5 to 50 μm and a solar monitoring channel. This paper describes the validation procedures and preliminary results. Each of the radiometer channels underwent extensive ground calibration, and the instrument packages include in-flight calibration facilities which, to date, show negligible changes of the instruments in orbit, except for gradual degradation of the suprasil dome of the shortwave wide FOV (about 4% per year). Measurements of the solar constant by the solar monitors, wide FOV, and medium FOV radiometers of two spacecraft agree to a fraction of a percent. Intercomparisons of the wide and medium FOV radiometers with the scanning radiometers show agreement of 1 to 4%. The multiple ERBE satellites are acquiring the first global measurements of regional scale diurnal variations in the Earth's radiation budget. These diurnal variations are verified by comparison with high temporal resolution geostationary satellite data.     

Quasi-biennial oscillation signals in outgoing long-wave radiation of the equator

In the present paper, the authors use wavelet transform technique to study time-series of outgoing long-wave radiation (OLR) anomaly at the equator during 1979–2005. The results show that quasi-biennial oscillation (QBO) signals exist in the OLR variation and the QBO cycle has remarkable temporal variability in its amplitude and phase. The periodic length of the QBO fluctuation is about 2.2-year before 1986. After that time, the length mainly changes from about 2.4- to 2.6-year. Analyzing the anomaly data set of 850 MB trade wind index (TWI) at west Pacific during this period, we have found that the obvious time-variations characteristics of the QBO cycle also exist in the TWI change at west Pacific and are in good consistence with that of the OLR change. The quasi-biennial fluctuation of the TWI change can explain that of the OLR change to a large extent.     

Clouds and Earth Radiant Energy System (CERES), a review: Past,present and future

The Clouds and Earth Radiant Energy System (CERES) project’s objectives are to measure the reflected solar radiance (shortwave) and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostationary meteorological satellites to account for changes of scenes between observations by the CERES radiometers.     

基于影像数据的冯·卡门撞击坑形貌分析

月球背面南极—艾肯（South Pole-Aitken,SPA）盆地内的冯·卡门（Von Kármán）撞击坑是“嫦娥4号”初步选定的着陆区,该区域的地形地貌分析是任务设计的一个重要环节。根据LOLA （Lunar Orbiter Laser Altimeter）高程数据和LROC（Lunar Reconnaissance Orbiter Camera）影像数据,建立了马尔科夫随机场模型,从聚类的角度对该区域的地形地貌进行了表示和分析。具体而言,利用模型中的似然函数对呈近似正态分布的观测数据进行了建模,模型的标记随机场则刻画了不同地物形貌间的空间关系,并通过概率推断求解出最终的聚类结果。实验结果表明,从聚类角度进行数据表示,可以更好地展示出冯·卡门撞击坑内低对比度区域的地形地貌;而通过设置不同的聚类数目,还有助于分析冯·卡门撞击坑内整体的地形分布与局部的典型地貌。     

基于数据网格化方法的低轨辐射带建模技术

地球辐射带中的高能带电粒子是引起航天器材料和器件性能退化甚至失效的主要空间环境因素.因此,航天器设计中所采用的辐射带模型的准确程度对于航天器的生存能力和航天任务的完成质量至关重要.在利用我国自主辐射带高能粒子探测数据进行的辐射带建模中,探测数据的空间网格化是一项非常重要的工作.介绍了我国辐射带探测数据的情况,以及辐射带建模的方法和步骤;重点研究了不同插值方法在低地球轨道(LEO)空间辐射带建模数据网格化中的应用,并开展了误差分析.研究结果表明:在各种常用的插值方法中,反距离加权法、自然邻点法和最近邻点法适合工程化应用.其中,反距离加权法生成的数据网格对粒子通量的反演结果精度最高,该方法采用低阶距离时得到的反演结果更为合理.      

Diurnal variation of earth radiation budget components above Africa and the neighboring Atlantic Ocean; Changes between 1983 and 1985, estimated from METEOSAT observations adjusted to ERBS data

METEOSAT observations in the thermal infrared “window” and “water vapor” channels, as well as in the visible channel, reveal diurnal variations over large areas which remain significant in the monthly means. The variations in the infrared correspond to diurnal cycles in the surface skin temperature (over land) and in cloud cover (over both land and sea) at various levels, and they must appear as a more or less significant diurnal variation in the integrated longwave emission to space of the Earth-atmosphere system. The diurnal cycle in the reflected shortwave radiation is influenced by these meteorological variations as well as by the astronomical cycle and the anisotropic reflectance. These must be taken into account in studies of Earth Radiation Budget variations. Using nearly simultaneous and spatially coincident pixel data from the ERBE scanner on ERBS and from METEOSAT in November 1984, we construct provisional transfer functions relating the narrow-band METEOSAT infrared observations to the longwave radiant exitance at the top of the atmosphere. We apply these transfer functions to the METEOSAT ISCCP B2 data sets for the summers of 1983–1985, and compare the resulting longwave radiant exitance estimates, with particular attention to the diurnal variation, which should be relatively insensitive to the inaccuracy inherent in applying the provisional (November 1984) transfer functions to the 1983–1985 data.     

Improvements in broadband planetary albedo estimates from narrowband NOAA satellite observations

New and current algorithms for estimating the broadband planetary albedo from NOAA satellite narrowband observations are testes by applying them to retrospective NOAA-9 AVHRR (Advanced Very High Resolution) data of 2 July 1985. For comparison, broadband SW fluxes taken by the Earth Radiation Budget Experiment (ERBE) instrument, also on NOAA-9 are used as reference values. In contrast to the current scene-independent model, the new algorithms are all scene-dependent, but differ in the way they are classified by surface, cloud amount and albedo indices. The current operational model produces a global bias of magnitude 5 W/m² and a strong latitudinal dependence in error. The scene-dependent algorithms yield global biases of less than ±3 W/m² and have little latitudinal dependence over most of the globe.     

Examining the use of the NeQuick bottomside and topside parameterizations at high latitudes

An examination of the high latitude performance of the bottomside and topside F-layer parameterizations of the NeQuick electron density model is presented using measurements from high latitude ionosonde and Incoherent Scatter Radar (ISR) facilities.For the bottomside, we present a comparison between modeled and measured B2Bot thickness parameter. In this comparison, it is seen that the use of the NeQuick parameterization at high latitudes results in significantly underestimated bottomside thicknesses, regularly exceeding 50%. We show that these errors can be attributed to two main issues in the NeQuick parameterization:(1) through the relationship relating foF2 and M3000F2 to the maximum derivative of F2 electron density, which is used to derive the bottomside thickness, and (2) through a fundamental inability of a constant thickness parameter, semi-Epstein shape function to fit the curvature of the high latitude F-region electron density profile.For the topside, a comparison is undertaken between the NeQuick topside thickness parameterization, using measured and CCIR-modeled ionospheric parameters, and that derived from fitting the NeQuick topside function to Incoherent Scatter Radar-measured topside electron density profiles. Through this comparison, we show that using CCIR-derived foF2 and M3000F2, used in both the NeQuick and IRI, results in significantly underestimated topside thickness during summer periods, overestimated thickness during winter periods, and an overall tendency to underestimate diurnal, seasonal, and solar cycle variability. These issues see no improvement through the use of measured foF2 and M(3000)F2 values. Such measured parameters result in a tendency for the parametrization to produce a declining trend in topside thickness with increasing solar activity, to produce damped seasonal variations, and to produce significantly overestimated topside thickness during winter periods.     

A space radiation shielding model of the Martian radiation environment experiment (MARIE)

The 2001 Mars Odyssey spacecraft was launched towards Mars on April 7, 2001. Onboard the spacecraft is the Martian radiation environment experiment (MARIE), which is designed to measure the background radiation environment due to galactic cosmic rays (GCR) and solar protons in the 20–500 MeV/n energy range. We present an approach for developing a space radiation-shielding model of the spacecraft that includes the MARIE instrument in the current mapping phase orientation. A discussion is presented describing the development and methodology used to construct the shielding model. For a given GCR model environment, using the current MARIE shielding model and the high-energy particle transport codes, dose rate values are compared with MARIE measurements during the early mapping phase in Mars orbit. The results show good agreement between the model calculations and the MARIE measurements as presented for the March 2002 dataset.     

Monte Carlo transport model comparison with 1A GeV accelerated iron experiment: heavy-ion shielding evaluation of NASA space flight-crew foodstuff.

Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively.     

How do interplanetary shock impact angles control the size of the geoeffective magnetosphere?

In this paper, we investigate temporal and spatial magnetosphere response to the impact of interplanetary (IP) shocks with different inclinations and speeds on the Earth’s magnetosphere. A data set with more than 500 IP shocks is used to identify positive sudden impulse (SI⁺) events as expressed by the SuperMAG partial ring current index. The SI⁺ rise time (RT), defined as the time interval between compression onset and maximum SI⁺ signature, is obtained for each event. We use RT and a model suggested by Takeuchi et al. (2002) to calculate the geoeffective magnetospheric distance (GMD) in the shock propagation direction as a function of shock impact angle and speed for each event. GMD is a generalization of the geoeffective magnetosphere length (GML) suggested by Takeuchi et al. (2002), defined from the subsolar point along the X line toward the tail. We estimate statistical GMD and GML values which are then reported for the first time. We also show that, similarly to well-known results for RT, the highest correlation coefficient for the GMD and impact angle is found for shocks with high speeds and small impact angles, and the faster and more frontal the shock, the smaller the GMD. This result indicates that the magnetospheric response depends heavily on shock impact angle. With these results, we argue that the prediction and forecasting of space weather events, such as those caused by coronal mass ejections, will not be accurately accomplished if the disturbances’ angles of impact are not considered as an important parameter within model and observation scheme capabilities.     

Robust extension of the simple sea-surface irradiance model to handle cloudy conditions for the global ocean using satellite remote sensing data

Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em^?2day^?1; and a mean net bias of 2.917 Em^?2day^?1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions.     

Comparison of the transport codes HZETRN,HETC and FLUKA for a solar particle event

The protection of astronauts and instrumentation from galactic cosmic rays and solar particle events is one of the primary constraints associated with mission planning in low earth orbit or deep space. To help satisfy this constraint, several computational tools have been developed to analyze the effectiveness of various shielding materials and structures exposed to space radiation. These tools are now being carefully scrutinized through a systematic effort of verification, validation, and uncertainty quantification. In this benchmark study, the deterministic transport code HZETRN is compared to the Monte Carlo transport codes HETC-HEDS and FLUKA for a 30 g/cm² water target protected by a 20 g/cm² aluminum shield exposed to a parameterization of the February 1956 solar particle event. Neutron and proton fluences as well as dose and dose equivalent are compared at various depths in the water target. The regions of agreement and disagreement between the three codes are quantified and discussed, and recommendations for future work are given.     

A biophysical model for estimating the frequency of radiation-induced mutations resulting from chromosomal translocations.

Gene mutations can be induced by radiation as a result of chromosomal translocations. A biophysical model is developed to estimate the frequency of this type of mutation induced by low-LET radiation. Mutations resulting from translocations are assumed to be formed by misrejoining of two DNA double strand breaks (DSB), one within the gene and one on a different chromosome. The chromosome containing the gene is assumed to occupy a spherical territory and does not overlap spatially with other chromosomes. Misrejoining between two DSB can occur only if the two DSB are closer than an interaction distance at the time of their induction. Applying the model to mutations of the hprt gene induced in G0 human lymphocyte cells by low-LET radiation, it is calculated that mutations resulting from translocations account for about 14% of the total mutations. The value of the interaction distance is determined to be 0.6 micrometers by comparing with the observed frequency of translocations in the X-chromosome.     

Theoretical consideration of the chemical pathways for radiation-induced strand breaks.

A theoretical approach to the understanding of the biochemical mechanisms of indirect action of ionizing radiation on SV40 DNA in aqueous solution is presented. The extent of OH attack on the sugar moiety and bases has been calculated. A realistic model for the DNA (in B form) based on available X-ray diffraction data is used and specific reaction sites for the OH radicals are obtained. A Monte Carlo scheme is used to follow the diffusion and reaction of the OH radicals. Effects of track structure have been considered and the single strand break D37 values for 14 MeV electrons (low-LET) and 670 MeV/u and 40 MeV/u neon particles are presented. Calculated results are in agreement with available experimental data. It has been found that regardless of the qualities of radiation, 80% of the OH attack on DNA is on the bases and 20% is on the deoxyribose. From probability considerations only, it appears that the number of double strand breaks varies linearly with dose.     

基于运动灵活性的蟑螂机器人机构参数优化

从仿生蟑螂机器人机构特点出发,基于运动灵活性,选择椭圆形身体布局,分别以单腿工作空间和整机雅克比矩阵的条件数倒数作为灵巧度指标,在兼顾运动灵活性和可靠性的基础上,对机器人机构参数进行优化配置,选择了最优的杆长比例.利用分析得出的优化尺寸建立ADAMS参数化仿真模型进行实验研究,仿真结果与理论分析相吻合,验证了优化配置的可行性和正确性,为样机的研制和机器人的驱动及控制等进一步研究奠定了基础,也为其他六足机器人的开发提供了参考.     

熔模精铸件凝固过程温度场的数值模拟

根据熔模精密铸造过程的传热特点,通过对铸型/环境边界及冒口/环境边界进行自然对流和辐射传热处理,改进了原有数值模拟系统,实现了对熔模铸造凝固过程温度场的数值模拟.对采用4种不同铸造工艺方案的阀体铸件凝固过程进行了数值模拟及缺陷预测,获得了与试验相一致的模拟结果.根据数值模拟结果,确定了进行批生产的铸造工艺方案.     

A new perspective of carcinogenesis from protracted high-LET radiation arises from the two-stage clonal expansion model.

When applied to the Colorado Plateau miner population, the two-stage clonal expansion (TSCE) model of radiation carcinogenesis predicts that radiation-induced promotion dominates radiation-induced initiation. Thus, according to the model, at least for alpha-particle radiation from inhaled radon daughters, lung cancer induction over long periods of protracted irradiation appears to be dominated by radiation-induced modification of the proliferation kinetics of already-initiated cells rather than by direct radiation-induced initiation (i.e., mutation) of normal cells. We explore the possible consequences of this result for radiation exposures to space travelers on long missions. Still unknown is the LET dependence of this effect. Speculations of the cause of this phenomenon include the suggestion that modification of cell kinetics is caused by a "bystander" effect, i.e., the traversal of normal cells by alpha particles, followed by the signaling of these cells to nearby initiated cells which then modify their proliferation kinetics.     

蒙皮热辐射特性对平流层浮空器氦气温度影响

分析了平流层球形超压浮空器在运行高度所受的各种环境辐射,研究浮空器处于热平衡状态时辐射传热、对流换热的作用规律,建立了浮空器的热平衡模型,分析太阳辐射、地面反照、地面辐射等环境辐照因素对浮空器全天各个时刻蒙皮材料和内部氦气平均温度影响,对比了吸收率、发射率和吸收发射比等辐射参数对浮空器热性能的影响.分析结果表明:具有低吸收发射比的蒙皮材料具有较好的热控效果;对于吸收发射比相同的蒙皮材料,具备低吸收率特性的蒙皮材料热控效果更为明显,更适用于长航时平流层超压浮空器.分析结果对浮空器蒙皮材料选择和总体设计具有指导意义.