Greenness Index from Phenocams Performs Well in Linking Climatic Factors and Monitoring Grass Phenology in a Temperate Prairie Ecosystem

Near-surface remote sensing (e.g., digital cameras) has played an important role in capturing plant phenological metrics at either a focal or landscape scale. Exploring the relationship of the digital image-based greenness index (e.g., Gcc, green chromatic coordinate) with that derived from satellites is critical for land surface process research. Moreover, our understanding of how well Gcc time series associate with environmental variables at field stations in North American prairies remains limited. This paper investigated the response of grass Gcc to daily environmental factors in 2018, such as soil moisture (temperature), air temperature, and solar radiation. Thereafter, using a derivative-based phenology extraction method, we evaluated the correspondence between key phenological events (mainly including start, end and length of growing season, and date with maximum greenness value) derived from Gcc, MODIS and VIIRS NDVI (EVI) for the period 2015-2018. The results showed that daily Gcc was in good agreement with ground-level environmental variables. Additionally, multivariate regression analysis identified that the grass growth in the study area was mainly affected by soil temperature and solar radiation, but not by air temperature. High frequency Gcc time series can respond immediately to precipitation events. In the same year, the phenological metrics retrieved from digital cameras and multiple satellites are similar, with spring phenology having a larger relative difference. There are distinct divergences between changing rates in the greenup and senescence stages. Gcc also shows a close relationship with growing degree days (GDD) derived from air temperature. This study evaluated the performance of a digital camera for monitoring vegetation phenological metrics and related climatic factors. This research will enable multiscale modeling of plant phenology and grassland resource management of temperate prairie ecosystems.     

Halin图的色数问题

Halin图G=T∪C,其中T为每一非悬挂点(内点)度数至少为3的平面树,C为连接T的所有悬挂点的圈.文章分别讨论了Halin图的星色数、面色数及分数色数.     

厦门台地倾斜年变畸变现象与1994年东山海外7.3级地震

1994年 9月 1 6日东山海外 7 3级地震前一年左右 ,厦门台地倾斜E -W分量年变发生严重畸变 ,正常年变规律图象明显被破坏 ,异常出现后 1 1个月 ,东山海外发生强震。该现象可以作为闽粤近海强震的一个重要前兆指标     

哈雷彗星主尾流的研究

哈雷彗星在日彗距较大时出现长而直的主彗尾（尾流），这是很有趣的。尾流一般是指等离子体尾流；但是，当地球接近彗星轨道面时，尘埃尾流可能叠加到主彗尾上。在一般感光波段宽的彗星底片上很难区分这两种尾流。本文选取哈雷彗星在不同日彗距的5条主尾流，作了光度测量和比较分析。得出沿各尾轴及其垂直方向几个截面的亮度分布、亮度半极大全宽、尾轴的视风差角和真风差角及彗尾长度。在所分析的蓝敏底片上，过近日点前的2个尾流肯定是等离子体尾流，而5个尾流的相似性以及其他证据说明它们主要都是等离子体尾流，尘埃彗尾的污染是次要的。     

Dark energy and the anthropic principle

The Hubble constant is split into two terms H = H₁ + H₂ , where H₁ is a decreasing function due to the Big Bang and the subsequent gravitational interaction that slows the expansion of the Universe and H₂ is an increasing function that corresponds to dark energy which accelerates this expansion. For T = 13.7 Gyr we prove that H₂(T) > 5 m/(yr AU). This is a quite large number and thus the impact of dark energy, which is spread almost everywhere uniformly, should be observable not only on large scales, but also in our Solar system. In particular, we show that Earth, Mars and other planets were closer to the Sun 4.5 Gyr ago. The recession speed ≈5.3 m/yr of the Earth from the Sun seems to be just right for an almost constant influx of solar energy from the origin of life on Earth up to the present over which time the Sun’s luminosity has increased approximately linearly. This presents further support for the Anthropic Principle. Namely, the existence of dark energy guarantees very stable conditions for the development of intelligent life on Earth over a period of 3.5 Gyr.     

地形畸变对偶极-偶极电阻率测深拟断面图的影响

偶极－偶极剖面方法是一种非常流行的物探方法,但就地形对该方法的实质性影响及修正研究得比较少.我们就几种典型的地形畸变情况进行了正演计算,并绘制了拟断面图.通过对这些图形分析,可以看到在地形畸变处的拟断面图不能反映地下地质体的情况,且有效拟断面图是不连续的,需要分段处理,分级解释.     

一种适用于视频全站仪的数码相机检校方法

直接线性变换法是相机检校中常用的一种方法,在此基础上提出一种可应用于视频全站仪的数码相机检校方法,通过改变像方元素的单位,就可不必考虑标准单位和像素单位间的转化因子问题。进一步讨论了像素尺寸大小对系统误差的影响,并对像素大小的必要测定精度进行了公式推导。试验结果表明,该方法可以获得较好的校准结果。     

有限差分偏移截断误差及其传递因子相角分析

讨论截断误差与误差传递因子相角的影响与决定因素 ,以寻求有限差分波动偏移的合理采样步长。用三种波场函数来模拟实际波场进行理论计算。结果表明 :时间采样步长Δt是截断误差的主导因素 ,空间采样步长Δx(横向 )和Δz(深度方向 ) ,尤其是Δx影响甚小。依据空间点变化时截断误差的变化规律 ,提出了变步长偏移法。分析误差传递因子相角等因素对有限差分波动方程偏移造成的相位畸变问题 ,找到相应规律。综合考虑截断误差及误差传递因子相角 ,给出了合理采样步长。     

色差对摄影测量精度的影响

在工业摄影测量中,由于相对精度较高,对相机的测量精度要求也相应增高。目前,常用的相机检校方法为10参数法,此方法未对色差的影响展开研究。本文通过将照片的R、G、B颜色分离,得到三组单色照片,再分别进行自检校光束法平差,对所得结果进行物方公共点转换后,发现三组单色照片与原始灰度照片的物方点精度相当,绿色分量照片处理精度较原始灰度照片有微小的提高。     

水温对棘胸蛙(Paa spinosa)蝌蚪行为及尾部皮肤和肝脏相关功能酶活力的影响

以1月龄棘胸蛙蝌蚪[体长(1.694±0.121)cm,体重(0.548±0.062)g]为实验对象,在观察水温对蝌蚪行为和尾部皮肤表观色泽Hunter L、A、B值影响的基础上,设置19°C(对照组)、21.5°C、23°C、24.5°C、26°C五个水温梯度,并以96h为水温胁迫时长,12d为水温恢复时长,研究了水温胁迫及恢复条件下棘胸蛙蝌蚪尾部皮肤ATP酶和抗氧化酶(SOD和CAT),以及肝脏抗氧化酶(SOD,CAT,GSH)活力的变化特征。结果表明:(1)棘胸蛙蝌蚪分布水层、集群状况、个体移动率均与其培育水温关系密切,14°C和26°C分别为可显著改变蝌蚪分布水层和个体移动率的水温临界;(2)L值可作为表征蝌蚪尾部皮肤感应培育水温的指示色差,水温26°C为致其发生显著改变的高温临界;(3)蝌蚪尾部皮肤ATP酶耐受水温的最适高限为24.5°C,适宜范围为21.5—24.5°C;(4)蝌蚪尾部皮肤和肝脏表露SOD酶活力的最适水温均为23°C,而表露CAT酶活力的最适水温则分别为23°C和24.5°C,水温26°C时肝脏SOD酶已表露受损;(5)蝌蚪肝脏表露GSH酶活力的最适水温为24.5°C,水温26°C为该酶表露受损的高温临界。