Passionate GISer, Remote Sensing Enthusiast and Point Cloud Processor
Harmful Algal Blooms有害藻华 What is algal blooms Algal blooms are the rapid growth of algae藻类 or cyanobacteria蓝藻 光合作用photosynthesis，真核生物eukaryotic organisms， 海洋微型有机物marine microorganisms Why it is harmful? recreational uses, toxins, ecosystem health What causes Algal Blooms Warm temperature Nitrogen and Phosphorus氮和磷 No wind How can RS help？ find algal blooms » detectable Most sensors have limitations»Resolution trade-offs: spatial, spectral, temporal True color is useful but not best Spectral library of cyanobacterial蓝藻 in a laboratory setting Chlorophyll-a & Phycocyanin (PC)藻蓝蛋白 unique for Cyano 内共生理论endosymbiotic theory：植物和藻类的叶绿体都是起源于一种蓝藻的内共生体 What causes Red-edge in terrestrial vegetation? absorption of blue (400 nm) and red (700nm) due to CHL-a/b» palisade: main site of photosynthetic absorption of red and blue light reflectance of near-infrared (>750nm) due to leaf scattering » spongy: cell geometries scatter and reflect near infrared light Why is there only little red-edge in cyanobacteria? 没有2，只有1，就是上一步的1,2 Compared to vegetation ==there is no NIR reflectance==这句话意思就是没有2 NDCI： Normalized difference chlorophy II index Spectral Shape(SS) Indices Floating Algae Index(FAI) Fluorescence Line Height (FLH)荧光线高度： FLH is a measure of the absolute amount of energy released by phytoplankton in the form of fluorescence. function of the radiation absorbed by phytoplankton and the probability for a given absorbed photon to be re-emitted as fluorescence. indicators for CHL-a and Phycocyanin(PC) which bands needed will be based on sensers and types Cyano Index(CI) Marine Litter Detection Scales of marine plastics Macroplastics (> 2.5 cm) Mesoplastics (5mm – 2.5cm) Microplastics (< 5mm) Marine Plastics are part of Marine Litter Marine Litter：垃圾 consists of solid materials that have been made or used by people and deliberately discarded or unintentionally lost in in marine and coastal environments, such as wood, metals, glass, rubber, textiles, paper and plastics (UNEP, 2005). Marine Debris：废弃物 as any aggregation of floating materials on the sea surface that may or may not contain marine litter of anthropogenic人为 origins. The impact of Marine Plastics on the Ecosystem Marine micro-plastics can have a toxic effect on fish and other aquatic life: reducing food intake, delaying growth, causing oxidative damage and abnormal behavior. Scales of Monitoring of Marine Litter with Remote Sensing In-situ studies: counting and measuring individual objects macro and meso-plastics UAV-based surveys: counting of individual macro plastic objects Satellite Earth Observation: detection of agglomerations of generic “marine debris” that can contain marine litter. River Plastic Monitoring Citizen Science-based beach surveys UAV Monitoring of Debris ==Remote Sensing Scales==各种尺度的优缺点 UAV-based Pro: High spatial resolution(detection of individual objects) Contra: expensive to scale, usually single acquisition, usually only RGB Satellite-based Pro: daily or weekly monitoring, multi-spectral signals Contra: low spatial resolution, complex mixed pixels (especially on beaches) Monitoring of Agglomerations聚集 through surface currents 为什么： Most objects are much smaller than the pixel size of available satellites Debris agglomerate in ==windrows== and ocean fronts废弃物聚集在==风堆==和海洋前缘 Remote Sensing Limitation: Trade-off between spatial and spectral resolution Floating Debris Index Floating Debris Index (FDI) as a Spectral Shape (SS) index designed for various heterogeneous marine debris.
Exercise 基于分层抽样的估计地图精度，估计面积和置信区间 1. Accuracy estimation based on sample counting 根据样本计数计算简单的混淆矩阵和准确性估计。如果使用简单随机抽样，基于该方法的地图精度计算是正确的。换句话说，所有样本单元被纳入样本的概率相同 2. Area weighted accuracy estimation for stratified sampling Why is converting the map to an equal area projection a necessary step?等积投影 An accuracy assessment which includes area weights and inclusion probabilities based on the size of the surface, would be more accurate if the area size is preserved.
Exercise geolocated coherence backscatter images analyze and interpret the imagery. SNAP Preparation Coherence Estimation First, we will co-register the input images so that their pixels match and interferometry can be performed. Then, we will calculate the coherence, merge the bursts of the images, and geocode the product. Backscatter Estimation Pixel Spacing (是single-look slant range and azimuth resolutions) 𝛿𝑔𝑟 = 𝛿𝑠𝑟 / sin 查资料的已知S1 SLC data的slant range= 2.7m, azimuth resolution = 22.5m 又已知最终的地理编码相干和后向散射产品的像素间距(pixel spacing)为20米 又假设incidence angle 是34 degree
Exercise 1. Visualization 直方图的分布类型 正态分布（Normal Distribution）： 也称为钟形曲线，是一种对称的分布，具有单一的峰值。大多数观测值集中在均值附近。 均匀分布（Uniform Distribution）： 所有数值具有相同的概率分布，直方图呈现为一个水平线。 正偏分布（Positively Skewed Distribution）： 也称为右偏分布，具有一个较长的右尾。大多数观测值集中在左侧，而右侧有一些较大的异常值。 指数分布（Exponential Distribution）： 呈现指数衰减的形状，通常用于描述随机事件的时间间隔。 双峰分布（Bimodal Distribution）： 具有两个峰值的分布，但不一定非对称。两个峰值可能具有相似或不同的高度。 对数正态分布（Log-Normal Distribution）： 对数正态分布的直方图在普通尺度上可能呈现非对称形状，但在对数尺度上更接近正态分布。 混合分布（Mixture Distribution）： 结合两个或更多不同分布的特征，可能导致多个峰值或非对称形状。 Stretch Compare “Stretch: 100%” (full range of pixel values), “Stretch: 90%” (only the range between the 5th and 95th percentile), and “Stretch 1 σ” (range between mean - 1 std and mean +1 std). 哪个更好地区分了IF和F，heterogeneous 啥的，还有pepper and salt effect 2. HHHV backscatter ratio HH-HV By subtracting HV value from the HH, the difference between the bimodal peaks is removed, bringing the distributions together. 水是相对均匀的，所以水的标准差很小 3. Analysing and describing class specific backscatter characteristics Jefferies-Mathuis distance(JMD) High JMD values between two classes means these two classes are more separatable. And when JMD value close to 0 means that they have similar values, which makes them difficult to distinguish for one another. Euclidean distance 4. Class specific scatter mechanisms Water: surface scatter Forest: Volume scatter Non Forest :The rest of the scattering mechanisms, measured in the HH, have lower intensity in the forest, but higher in the non-forested areas, resulting in higher contrast between these classes. Inundated Forest: HH 疯狂double bounce, HV就跟Forest差不多The signal over inundated forest will be reflected perpendicularly from the smooth water surface to the tree trunks and from the tree trunks it would be sent back to the sensor. L-band 和C-band哪个更适合这个研究forest L!!! Non-forest is in this study area referring to the mines, which have rougher soil surfaces & second vegetation (grass), forest debris (fallen branches). Rougher surfaces would have more interaction with C-band signal, because L-band signal does not see the individual smaller rocks on the soil surface. Taking that into account, the C-band would have less contrast between the canopies and non-forested areas. PPT high backscatter» both VV and VH greener in tropical »more volume purple » high VV, low VH» high surface, low volume ![[27e4f309fb3e9211b0a65021e5cfcc5.png]] Radar Fundamentals all radar system is SAR»Side-looking airborne radar (SLAR) incidence angle will change with near range/far range VH == HV Backscatter often given in 𝜎0(sigma nought» surface) or γ0(gamma nought»stable) in dB scale(small) 不懂回去找 optical vs radar, Side-looking airborne radar, radar geometry, ascending and descending orbits, wavelength, polarisation, Radar measurement, gemetric effects(layover>shadow, foreshortening>weak return) speckle Scattering mechanisms of forest ==Backscattered== signal mainly results from: ● Volume scattering ● Surface scattering ● Single-bounce scattering ● Double-bounce scattering ==Relative contributions== depend on: ● Surface roughness ● Dielectric properties of the medium ==All of these factors== depend on: ● The radar wavelength ● The polarization ● The incidence angle Surface scattering The moisture content (dielectric constant) of the medium governs the strength of the backscatter Surface roughness Shell’s law 相对粗糙度: ==same surface: rougher in short wavelength, smoother in long wavelength== Dielectric Constant介电常数 Complex dielectric Constant (ε) ratio of the permittivity（介电常数） of a material to the permittivity of free space 自由空间的介电常数和材料的介电常数相比 In other words: indicator of the ==reflectivity of a material== ==increasing ε leads to increasing backscatter== 例子 介电常数的波动(fluctuation) Water is purple, because the wave of the water » wind Soil: large ε fluctuations (rain, dry) Forest: stable ε (saturated forest canopy) Ancient river network» dry sand/dry snow»Complex dielectric Constant (ε)=2-3» high permittivity Strong drop under freezing conditions» from water(80) to ice(3-4) Volume scattering Concept: Inhomogeneous medium (canopy): Each inhomogeneity (leaves, branches) scatters incident wave in different directions Multiple scattering leads to depolarisation去极化 and attenuation 衰退of the signal ==Main source of VH and HV scattering== Increasing backscatter with increasing dielectric constant Depolarization Change in the orientation of the electric field during a reflection with curved scatters’ such as disc or cylinders 圆柱体 弯曲散射体(如圆盘或圆柱体)反射时电场方向的变化。 Mainly occurs due to multiple scattering Single-bounce scattering Direct scattering from tree elements ==VV > HH== Some depolarisation, but very small (VH, HV) Double-bounce scattering Concept: Two smooth surfaces form a right angle facing the radar beam ==HH > VV== Some depolarisation; HV and VH backscatter > 0 (but very weak) Forest structure Penetration depth and key forest scatterers Understory » Volume Mangroves HH double bounce»Brightening of the forest during inundation
Exercise Preprocessing Creating a raster brick and cleaning the MODIS data using the reliability layer
SDG(Sustainable Development Goals) 11 5 main areas: Social development Economic development Environmental sustainability Peaceful, just and inclusive societies Partnership Make cities and human settlements inclusive, safe, resilient and sustainable urban : population/building density Urban areas defined Degree of urbanization based on geographical contiguity邻里临近度 and population density人口密度把地方行政单位划分为cities, towns and suburbs and rural areas 基于 1km^2 的population grid cells» 其用于分类行政» urban center, urban cluster, rural grid cells Urban Themes Urban land change, Urban Green Space, Urban Heat Island, Urban Nighttime Lights Urban Land Change How :Growing, shrinking, intensifying, restructuring Global products (4) Global Urban Footprint Global Rural-Urban Mapping Project GlobalLand30 Global Human Settlements Layer
Exercise 4 Why UAV thermal imaging can monitor vegetation stress? It sensitivity to disruptions in stomatal conductance Stage 1: Data exploration and emissivity correction Highest temperature and lowest(最高温最亮) Ground control points deployed to aid with the survey have the highest temperature. Artificial materials tend to be good absorbers, meaning they heat up quicker than natural surfaces. Areas with bare soil also have very high temperature values – soils have low relatively thermal inertia, warming up quickly during daytime. Vegetated areas have lowest temperatures in the image. This is because plants actively lower their temperature through transpiration. Surface temperature irrigated field » low temperature non-irrigated field » high temperature bare soil has low thermal inertia»heats up rapidly during the day Water has high thermal inertia» remain stable temperature during the day so, water is cooler than bare soil. 求 minimum and maximum emissivity value ɛ(λ) + ρ(λ) + τ(λ) = 1 Separate vegetated areas from bare soil NDVI thresholding, unsupervised/supervised classification, image segmentation. After emissivity correction Emissivity correction will increase recorded temperature values of both vegetation canopies and soil. 变化的裸土的温度差比冠层变化的差异大The impact of the correction will be more evident for soil (i.e. larger change in the retrieved temperatures)because of the lower emissivity value being used.
Exercise 一. SfM photogrammetry of UAV data in Agisoft Metashape 1. Import photos 为什么不用起飞和降落时候的照片？ The photos from take off and landing have already been removed, so all photos are at the same height level. ==However, the lines are not really parallel, but they are a bit skewed==. Dependent on the field of view of the camera this may cause issues with the overlap and with having enough different viewing angles over the entire scene. 2. Project with UTM projection Geographic data is often presented in a projected coordinate system, in order to visualize 3D data in two dimensions (on your screen). In this process longitude/latitude is converted to (x,y) coordinates.
Physical foundations (a) Draw a (triangular) prism and then draw the path of a beam of light that enters at an incidence angle of 30 degrees, travels through the prism and leaves it at the opposite wall. (b) Does red and blue light follow the same path? What is the reason for your answer?