MODIS/Aqua Calibrated Radiances 5-Min L1B Swath 250m - NRT

The 250 meter MODIS Level 1B Near Real Time (NRT) data set contains calibrated and geolocated at-aperture radiances for 2 discrete bands located in the 0.62 to 0.88 micron region of the electromagnetic spectrum. These data are generated from the MODIS Level 1A scans of raw radiance and in the process converted to geophysical units of W / (m^2 um sr). In addition, the Earth Bi-directional Reflectance Distribution Function (BRDF) may be determined for these solar reflective bands through knowledge of the solar irradiance (e.g., determined from MODIS solar diffuser data, and from the target illumination geometry). Additional data are provided including quality flags, error estimates and calibration data. Channel locations for the MODIS 250 meter data are as follows: Band Center Wavelength (um) Primary Use ---- ---------------------- ----------- 1 0.620 - 0.670 Land/Cloud Boundaries 2 0.841 - 0.876 Land/Cloud Boundaries Separate L1B products are available for the five 500 m resolution channels (MYD02HKM) and the twenty-nine 1 km resolution channels (MYD021KM). For the 500 m product, there are actually seven channels available since the data from the two 250 m channels have been aggregated to 500 m resolution. Similarly, for the 1 km product, all 36 MODIS channels are available since the data from the two 250 m and five 500 m channels have been aggregated into equivalent 1 km pixel values. Spatial resolution for pixels at nadir is 250 m, degrading to 1.2 km in the along-scan direction and 0.5 km in the along-track direction for pixels located at the scan extremes. A 55 degree scanning pattern at the EOS orbit of 705 km results in a 2330 km orbital swath width and provides global coverage every one to two days. A single MODIS Level 1B 250 m granule will contain a scene built from 203 scans sampled 5416 times in the cross-track direction, corresponding to approximately 5 minutes worth of data; thus 288 granules will be produced per day. Since an individual MODIS scan will contain 40 along-track spatial elements for the 250 m channels, the scene will be composed of (5416 x 8120) pixels, resulting in a spatial coverage of (2330 km x 2040 km). Due to the MODIS scan geometry, there will be increasing scan overlap beyond about 17 degrees scan angle. To summarize, the MODIS L1B 250 m data product consists of: 1. Calibrated radiances and uncertainties for (2) 250 m reflected solar bands 2. Subsampled geolocation at every 4th 250 m pixel across and along track, i.e., a geolocation point every kilometer 3. Satellite and solar angles subsampled at the above frequency 4. Calibration data for all channels (scale and offset) 5. Comprehensive set of file-level metadata summarizing the spatial, temporal and parameter attributes of the data, as well as auxiliary information pertaining to instrument status and data quality characterization The MODIS L1B 250 m data are stored in the Earth Observing System Hierarchical Data Format (HDF-EOS) which is an extension of HDF as developed by the National Center for Supercomputer Applications (NCSA) at the University of Illinois. A typical file size will be approximately 170 MB. Environmental information derived from MODIS L1B measurements will offer a comprehensive and unprecedented look at terrestrial, atmospheric, and ocean phenomenology for a wide and diverse community of users throughout the world. The Shortname for this product is MYD02QKM

该250米MODIS一级B近实时（NRT）数据集包含位于电磁谱0.62至0.88微米区域的两个离散波段在入射孔径处的校准和地理定位辐射度。这些数据源自MODIS一级A的原始辐射度扫描，并在转换过程中以W/(m²μm sr)的地球物理单位表示。此外，通过了解太阳辐照度（例如，由MODIS太阳漫射器数据和目标照度几何形状确定），可以确定这些太阳反射波段的大气双向反射分布函数（BRDF）。此外，还提供了包括质量标志、误差估计和校准数据在内的附加数据。MODIS 250米数据的通道位置如下：波段 中心波长（um） 主要用途 ---- ---------------------- ----------- 1 0.620 - 0.670 陆地/云边界 2 0.841 - 0.876 陆地/云边界 分离的L1B产品适用于五个500米分辨率通道（MYD02HKM）和二十九个1公里分辨率通道（MYD021KM）。对于500米产品，实际上有七个通道可用，因为两个250米通道的数据已汇总为500米分辨率。同样，对于1公里产品，所有36个MODIS通道均可用，因为两个250米和五个500米通道的数据已汇总成等效的1公里像素值。像素在正下方的空间分辨率为250米，在扫描方向上降至1.2公里，在沿轨道方向上降至0.5公里。在地球观测系统（EOS）轨道705公里处的55度扫描模式导致2330公里的轨道带宽度，并可实现每1至2天一次的全球覆盖。单个MODIS一级B 250米数据块将包含由203个扫描组成的一个场景，这些扫描在横跨轨道方向上采样5416次，相当于大约5分钟的数据；因此，每天将产生288个数据块。由于单个MODIS扫描将包含250米通道的40个沿轨道空间元素，场景将由（5416 x 8120）个像素组成，从而实现（2330 km x 2040 km）的空间覆盖。由于MODIS扫描几何形状，扫描重叠将在大约17度扫描角后增加。总之，MODIS一级B 250米数据产品包括：1. 250米反射太阳波段（2个）的校准辐射度和不确定性2. 在横跨和沿轨道方向上每隔4个250米像素进行子采样地理定位，即每公里一个地理定位点3. 在上述频率下子采样卫星和太阳角度4. 所有通道的校准数据（比例尺和偏移量）5. 一套全面的文件级元数据，总结了数据的空间、时间和参数属性，以及有关仪器状态和数据质量表征的辅助信息MODIS一级B 250米数据存储在地球观测系统分层数据格式（HDF-EOS）中，它是伊利诺伊大学国家超级计算应用中心（NCSA）开发的HDF的扩展。典型文件大小约为170 MB。从MODIS一级B测量中获得的环境信息将为全球广泛且多样化的用户群体提供一个全面且前所未有的陆地、大气和海洋现象的视角。该产品的短名为MYD02QKM。