MODIS/Aqua Cloud Mask and Spectral Test Results 5-Min L2 Swath 250m and 1km - NRT

The MODIS level-2 cloud mask product is a global product generated for both daytime and nighttime conditions at 1-km spatial resolution (at nadir) and for daytime at 250-m resolution. The algorithm employs a series of visible and infrared threshold and consistency tests to specify confidence levels that an unobstructed view of the Earth's surface is observed.

The Terra MODIS Photovoltaic (PVLWIR) bands 27-30 are known to experience an electronic crosstalk contamination. The influence of the crosstalk has gradually increased over the mission lifetime, causing for example, earth surface features to become prominent in atmospheric band 27, increased detector striping, and long term drift in the radiometric bias of these bands. The drift has compromised the climate quality of C6 Terra MODIS L2 products that depend significantly on these bands, including cloud mask (MOD35), cloud fraction and cloud top properties (MOD06), and total precipitable water (MOD07). A linear crosstalk correction algorithm has been developed and tested by MCST.The electronic crosstalk correction was made to the calibration algorithm for bands 27-30 and implemented into C6.1 operational L1B processing. This implementation greatly improves the performance of the cloud mask.

The shortname for this Level-2 MODIS cloud mask product is MYD35_L2 and the principal investigator for this product is MODIS scientist Dr. Paul Menzel ( [e-mail]). MYD35_L2 product files are stored in Hierarchical Data Format (HDF-EOS). Each of the 9 gridded parameters is stored as a Scientific Data Set (SDS) within the HDF-EOS file. The Cloud Mask and Quality Assurance SDS's are stored at 1 kilometer pixel resolution. All other SDS's (those relating to time, geolocation, and viewing geometry) are stored at 5 kilometer pixel resolution.

MYD35_L2 Data Group and Parameters:

Spatial and Temporal Resolution:

Latitude and Longitude
Scan start time

Solar and Sensor Viewing Geometry:

Solar zenith and Solar azimuth angle
Sensor zenith and Sensor azimuth angle

Science Parameters:
Cloud Mask (1km)
Cloud Mask (250 m)

Quality Assurance Parameters:
Quality Assurance Flags (1km)

Link to the MODIS homepage for more data set information:

https://modis-atmos.gsfc.nasa.gov/products/cloud-mask

Link to the MODIS homepage for C6.1 changes:

https://modis-atmos.gsfc.nasa.gov/documentation/collection-61

MODIS二级云掩膜产品是一款全球性产品，旨在昼夜两种条件下以1公里空间分辨率（正对点）生成，并在白天以250米分辨率生成。该算法通过一系列可见光和红外阈值及一致性检验，以确定观测到地球表面无遮挡视野的置信水平。Terra MODIS光伏（PVLWIR）波段27-30已知存在电子串扰污染问题。串扰的影响在任务生命周期内逐渐增强，例如，导致地表特征在大气波段27中突出，增加了探测器条纹，以及这些波段辐射偏移的长期漂移。这种漂移损害了依赖于这些波段的大量C6 Terra MODIS L2产品的气候质量，包括云掩膜（MOD35）、云量和云顶特性（MOD06）以及总可降水（MOD07）。MCST开发并测试了一种线性串扰校正算法，对波段27-30的校准算法进行了电子串扰校正，并将其实施于C6.1操作L1B处理中。这一实施显著提高了云掩膜的性能。该二级MODIS云掩膜产品的简称是MYD35_L2，该产品的首席研究员是MODIS科学家保罗·门泽尔博士（[e-mail]）。MYD35_L2产品文件存储在层次数据格式（HDF-EOS）中。每个9个网格参数均作为科学数据集（SDS）存储在HDF-EOS文件中。云掩膜和质量保证SDS存储在1公里像素分辨率。所有其他SDS（与时间、地理位置和观察几何有关）均存储在5公里像素分辨率。MYD35_L2数据组和参数：空间和时间分辨率：纬度和经度、扫描开始时间；太阳和传感器观察几何：太阳天顶角和太阳方位角、传感器天顶角和传感器方位角；科学参数：云掩膜（1公里）、云掩膜（250米）；质量保证参数：质量保证标志（1公里）。更多数据集信息请访问MODIS主页：

https://modis-atmos.gsfc.nasa.gov/products/cloud-mask

C6.1变更请访问MODIS主页：

https://modis-atmos.gsfc.nasa.gov/documentation/collection-61