MODIS/Terra Calibrated Radiances 5-Min L1B Swath 500m - NRT

The 500 meter MODIS Level 1B Near Real Time (NRT) data set contains calibrated and geolocated at-aperture radiances for 7 discrete bands located in the 0.45 to 2.20 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). Additional data are provided including quality flags, error estimates and calibration data.

Visible, shortwave infrared, and near infrared measurements are only made during the daytime (except band 26), while radiances for the thermal infrared region (bands 20-25, 27-36) are measured continuously.
Channel locations for the MODIS 500 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
3 0.459 - 0.479 Land/Cloud Properties
4 0.545 - 0.565 Land/Cloud Properties
5 1.230 - 1.250 Land/Cloud Properties
6 1.628 - 1.652 Land/Cloud Properties
7 2.105 - 2.155 Land/Cloud Properties

Channels 1 and 2 have 250 m resolution, channels 3 through 7 have 500 m resolution. However, for the MODIS L1B 500 m product, the 250 m band radiance data and their associated uncertainties have been aggregated to 500m resolution. Thus the entire channel data set has been co-registered to the same spatial scale in the 500 m product. Separate L1B products are available for the 250 m resolution channels (MOD02QKM) and 1 km resolution channels (MOD021KM). For the latter product, the 250 m and 500 m channel data (bands 1 through 7) have been aggregated into equivalent 1 km pixel values.

Spatial resolution for pixels at nadir is 500 km, degrading to 2.4 km in the along-scan direction at the scan extremes. However, thanks to the overlapping of consecutive swaths and respectively pixels there, the resulting resolution at the scan extremes is about 1 km. 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 500 m granule will contain a scene built from 203 scans sampled 2708 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 20 along-track spatial elements for the 500 m channels, the scene will be composed of (2708 x 4060) 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 20 degrees scan angle.

To summarize, the MODIS L1B 500 m data product consists of:

1. Calibrated radiances, uncertainties and number of samples for (2) 250 m reflected solar bands aggregated to 500 m resolution

2. Calibrated radiances and uncertainties for (5) 500 m reflected solar bands

3. Geolocation for 1km pixels, that must be interpolated to get 500 m pixel locations. For the relationship of 1km pixels to 500m pixels, see the Geolocation ATBD ttp://modis.gsfc.nasa.gov/data/atbd/atbd_mod28_v3.pdf .

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 Users requiring all geolocation and solar/satellite geometry fields at 1km resolution can obtain the separate MODIS Level 1 Geolocation product (MOD03) from LAADS http://ladsweb.nascom.nasa.gov/ .

The Shortname for this product is MOD02HKM and is stored in the Earth Observing System Hierarchical Data Format (HDF-EOS). A typical MOD02HKM file size is approximately 135 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.

See the MODIS Characterization Support Team webpage for more C6 product information at:

http://mcst.gsfc.nasa.gov/l1b/product-information

or visit Science Team homepage at:
http://modis.gsfc.nasa.gov/data/dataprod/

该500米MODIS一级B近实时(NRT)数据集包含了位于电磁谱0.45至2.20微米区域内的7个离散波段的开孔辐射亮度，这些数据经过校准和地理定位。数据源自MODIS一级A的原始辐射亮度扫描，并在处理过程中转换为物理单位W/(m² μm sr)。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信息。在白昼时段进行可见光、短波红外和近红外测量（除波段26外），而热红外区域（波段20-25，27-36）的辐射亮度则持续测量。MODIS 500米数据的通道位置如下：

波段 中心波长(μm) 主要用途
---- ---------------------- -----------
1 0.620 - 0.670 陆地/云边界
2 0.841 - 0.876 陆地/云边界
3 0.459 - 0.479 陆地/云特性
4 0.545 - 0.565 陆地/云特性
5 1.230 - 1.250 陆地/云特性
6 1.628 - 1.652 陆地/云特性
7 2.105 - 2.155 陆地/云特性

通道1和2具有250米分辨率，通道3至7具有500米分辨率。然而，对于MODIS L1B 500米产品，250米波段辐射亮度数据和相关的误差已汇总至500米分辨率。因此，整个通道数据集在500米产品中已进行空间对准。对于250米分辨率通道（MOD02QKM）和1公里分辨率通道（MOD021KM）可分别获取单独的L1B产品。对于后者产品，250米和500米通道数据（波段1至7）已汇总为等效的1公里像素值。像素在正下方的空间分辨率为500公里，在扫描端点的扫描方向上降至2.4公里。然而，得益于连续条带和相应像素的重叠，扫描端点的分辨率约为1公里。EOS轨道上的55度扫描模式导致705公里的轨道条带宽度为2330公里，并可实现每1至2天一次的全球覆盖。单个MODIS一级B 500米数据块将包含由203个扫描组成的一个场景，在横越轨道方向上采样2708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500米通道的20个沿轨道空间元素，因此场景将由(2708 x 4060)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20度扫描角后增加。

概括而言，MODIS L1B 500米数据产品包括以下内容：

1. 将(2)个250米反射太阳波段汇总至500米分辨率的校准辐射亮度、不确定性和样本数量

2. (5)个500米反射太阳波段的校准辐射亮度和不确定性

3. 1公里像素的地理位置，必须插值以获得500米像素位置。有关1公里像素与500米像素的关系，请参阅地理位置ATBD ttp://modis.gsfc.nasa.gov/data/atbd/atbd_mod28_v3.pdf。

4. 所有通道的校准数据（比例尺和偏移量）

5. 汇总数据的空间、时间和参数属性的文件级元数据，以及与仪器状态和数据质量表征相关的辅助信息。需要所有1公里分辨率地理位置和太阳/卫星几何字段的用户可以从LAADS获取单独的MODIS一级地理位置产品（MOD03） http://ladsweb.nascom.nasa.gov/ 。

该产品的短名为MOD02HKM，并存储在地球观测系统层次数据格式（HDF-EOS）中。一个典型的MOD02HKM文件大小约为135 MB。从MODIS L1B测量中提取的环境信息将为全球范围内广泛而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。

有关更多C6产品信息，请访问MODIS表征支持团队网页：

http://mcst.gsfc.nasa.gov/l1b/product-information

或访问科学团队主页：

http://modis.gsfc.nasa.gov/data/dataprod/