Hyperspectral surveys of Ningaloo Marine Park, Western Australia

HyVista Corporation was contracted by AIMS to acquire hyperspectral data over Ningaloo Marine Park in Western Australia. A total of 67 HyMap image strips were acquired, within 11 individual Blocks (A-K), between the 20th of April and the 2nd of May, 2006. The HyMap data products that have been delivered are radiance, reflectance and geocorrected data.The data acquisition was conducted in individual blocks. Each HyMap data block was acquired in one sortie and whenever possible HyVista tried to fly more then one block in one day. Due to survey time restrictions, Block F was acquired on two different days to allow for optimal sun angles. The HyMap survey was planned to cover the water areas to the 20m bathymetry line. Two blocks (G and F) cover it all the way to the 50m line. The survey was also extended to cover the Muiron Islands and the land area past Exmouth town. The area covered total 3400 square kilometers collected at 3.5m pixel size.Derived bathymetry and habitat models. The HyMap sensor is an airborne imaging system that is used for earth resources remote sensing. It records a digital image of the earth's sunlit surface underneath the aircraft but unlike standard aerial cameras, the HyMap records images in a large number of wavelengths. In essence, the HyMap is an airborne spectrometer and like spectrometers used in analytical chemistry, it can detect and identify materials by the spectral features contained in the recorded data.The HyMap records an image of the earth's surface by using a rotating scan mirror which allows the image to build line by line as the aircraft flies forward. The reflected sunlight collected by the scan mirror is then dispersed into different wavelengths by four spectrometers in the system. The spectral and image information from the spectrometers is digitized and recorded on tape.The HyMap sensor utilizes four 32-element detector arrays (1 Si, 3 liquid-nitrogen cooled InSb) to provide 126 spectral channels covering the 450nm to 2500nm spectral range over a 512 pixel swath.To minimize distortion induced in the image by aircraft pitch, roll and yaw motions, the HyMap is mounted in a gyro-stabilized platform (Zeiss SM2000). While the platform minimizes the effects of aircraft motion, small image distortions remain. These residual motions are monitored with a 3 axis gyro, 3 axis accelerometer system (IMU-inertial monitoring unit). The system currently used with the HyMap is a Boeing C-MIGITS II.Associated with the actual HyMap optical system is an electronics sub-system which is rack mounted in the aircraft. This electronics sub-system provides the sensor with power and contains a computer system that controls the data acquisition process. There is a touch screen monitor used by the operator to set data acquisition parameters, start and stop recording, view the image as it is being acquired and review various engineering status indicators (power, temperature etc).The HyMap system has been designed to operate in aircraft that have standard aerial photo-ports. The angular width of the recorded image is 61.3 degrees or about 2.3 km when operating 2000m above ground level. Typically, the spatial resolution achieved with the HyMap is in the range 3 to 10 m. For the Ningaloo survey (3.5 m pixel size) the average survey altitude was about 1400m-1500m above ground with a swath width of 1.8 km.

海维斯塔公司（HyVista Corporation）受AIMS委托，在西澳大利亚州的宁格罗海洋公园（Ningaloo Marine Park）开展高光谱数据（hyperspectral data）采集工作。2006年4月20日至5月2日期间，共采集67条HyMap影像条带，涵盖11个独立区块（A至K）。
交付的HyMap数据产品包含辐射亮度（radiance）、反射率（reflectance）与地理校正（geocorrected）数据。数据采集按独立区块开展，每个HyMap数据区块均通过单次飞行架次（sortie）完成；条件允许时，HyVista会尝试在单日完成多个区块的飞行作业。受航测时间限制，区块F分两日完成采集，以获取最优太阳高度角（sun angles）。
本次HyMap航测计划覆盖至20米水深等深线的水域区域，其中区块G与F的覆盖范围延伸至50米水深等深线。此外，航测范围还扩展至缪恩群岛（Muiron Islands）以及埃克斯茅斯镇（Exmouth town）周边的陆地区域，总覆盖面积达3400平方千米，像素尺寸为3.5米。衍生得到水深与生境模型（bathymetry and habitat models）。
HyMap传感器是一款用于地球资源遥感（earth resources remote sensing）的机载成像系统（airborne imaging system）。与常规航空相机不同，它可在多个光谱波段采集飞机下方受阳光照射的地球表面数字影像。本质上，HyMap属于机载光谱仪（spectrometer），与分析化学（analytical chemistry）中使用的光谱仪类似，可通过记录数据中的光谱特征识别并区分地物材质。
HyMap通过旋转扫描镜（rotating scan mirror）逐线构建影像：当飞机向前飞行时，扫描镜收集的反射太阳光经系统内的4台光谱仪色散为不同波长。光谱与影像信息经数字化后记录于磁带中。HyMap传感器采用4组32元探测器阵列（detector arrays，1组硅（Si）探测器、3组液氮制冷锑化铟（InSb）探测器），可提供126个光谱通道，覆盖450nm至2500nm的光谱范围（spectral range），条带宽度包含512个像元。
为减少飞机俯仰（pitch）、滚转（roll）和偏航（yaw）运动带来的影像畸变，HyMap搭载在蔡司SM2000（Zeiss SM2000）陀螺稳定平台（gyro-stabilized platform）上。尽管该平台可缓解飞机运动的影响，但仍存在小幅影像畸变。此时通过三轴陀螺、三轴加速度计系统（IMU-惯性测量单元，inertial monitoring unit）监测残余运动（residual motions），当前与HyMap配套使用的惯性系统为波音C-MIGITS II（Boeing C-MIGITS II）。
与HyMap光学系统配套的电子子系统（electronics sub-system）采用机架式安装于飞机内，可为传感器提供电源，并搭载用于控制数据采集流程的计算机系统。操作人员通过触摸屏显示器（touch screen monitor）设置数据采集参数、启动/停止记录、查看实时采集的影像，并监控各类工程状态指示器（engineering status indicators，如电源、温度等）。
HyMap系统可适配搭载标准航空摄影接口（standard aerial photo-ports）的飞机，其记录影像的视场角（angular width）为61.3度，在离地高度（above ground level）2000米时，条带宽度约为2.3千米。HyMap的典型空间分辨率（spatial resolution）范围为3至10米。本次宁格罗航测采用3.5米像素尺寸，平均飞行高度约为1400米至1500米离地高度，条带宽度为1.8千米。