VIIRS Day/Night Band Nighttime Lights: monthly and annual average radiance composite images

The Earth Observations Group (EOG) is producing a version 1 suite of average radiance composite images using nighttime data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB). Prior to averaging, the DNB data is filtered to exclude data impacted by stray light, lightning, lunar illumination, and cloud-cover. Cloud-cover is determined using the VIIRS Cloud Mask product (VCM). In addition, data near the edges of the swath are not included in the composites (aggregation zones 29-32). Temporal averaging is done on a monthly and annual basis. The version 1 series of monthly composites has not been filtered to screen out lights from aurora, fires, boats, and other temporal lights. However, the annual composites have layers with additional separation, removing temporal lights and background (non-light) values. The version 1 products span the globe from 75N latitude to 65S. The products are produced in 15 arc-second geographic grids and are made available in geotiff format as a set of 6 tiles. The tiles are cut at the equator and each span 120 degrees of latitude. Each tile is actually a set of images containing average radiance values and numbers of available observations. In the monthly composites, there are many areas of the globe where it is impossible to get good quality data coverage for that month. This can be due to cloud-cover, especially in the tropical regions, or due to solar illumination, as happens toward the poles in their respective summer months. Therefore, it is imperative that users of these data utilize the cloud-free observations file and not assume a value of zero in the average radiance image means that no lights were observed. The version 1 monthly series is run globally using two different configurations. The first excludes any data impacted by stray light. The second includes these data if the radiance vales have undergone the stray-light correction procedure (Reference). These two configurations are denoted in the filenames as "vcm" and "vcmsl" respectively. The "vcmsl" version, that includes the stray-light corrected data, will have more data coverage toward the poles, but will be of reduced quality. It is up to the users to determine which set is best for their applications. The annual versions are only made with the “vcm” version, excluding any data impacted by stray light. Filenaming convention: The version 1 composite products have 7 filename fields that are separated by an underscore "_". Internal to each field there can be an additional dash separator "-". These fields are followed by a filename extension. The fields are described below using this example filename: SVDNB_npp_20140501-20140531_global_vcmcfg_v10_c201502061154.avg_rade9 Field 1: VIIRS SDR or Product that made the composite "SVDNB" Field 2: satellite name "npp" Field 3: date range "20140501-20140531" Field 4: ROI "global" Field 5: config shortname "vcmcfg" Field 6: version "v10" is version 1.0 Field 7: creation date/time Extension: avg_rade9 The annual products can have other values for the config shortname (Field 5). They are: "vcm-orm" (VIIRS Cloud Mask - Outlier Removed) This product contains cloud-free average radiance values that have undergone an outlier removal process to filter out fires and other ephemeral lights. "vcm-orm-ntl" (VIIRS Cloud Mask - Outlier Removed - Nighttime Lights) This product contains the "vcm-orm" average, with background (non-lights) set to zero. "vcm-ntl" (VIIRS Cloud Mask - Nighttime Lights) This product contains the "vcm" average, with background (non-lights) set to zero. Data types/formats: To reach the widest community of users, files are delivered in compressed tarballs, each containing a set of 2 geotiffs. Files with extensions "avg_rade9" contain floating point radiance values with units in nanoWatts/cm2/sr. Note that the original DNB radiance values have been multiplied by 1E9. This was done to alleviate issues some software packages were having with the very small numbers in the original units. Files with extension "cf_cvg" are integer counts of the number of cloud-free coverages, or observations, that went in to constructing the average radiance image. Files with extension “cvg” are integer counts of the number of coverages or total observations available (regardless of cloud-cover). Credit: When using the data please credit the product generation to the Earth Observation Group, Payne Institute for Public Policy.地球观测小组（Earth Observations Group，EOG）正基于可见红外成像辐射计套件（Visible Infrared Imaging Radiometer Suite，VIIRS）的日间/夜间波段（Day/Night Band，DNB）夜间数据，制作版本1的平均辐射度合成图像套件。 在进行平均计算前，需对DNB数据进行滤波处理，以排除受杂散光、闪电、月球光照以及云覆盖影响的数据。云覆盖情况通过VIIRS云掩膜产品（VIIRS Cloud Mask product，VCM）判定。此外，扫描带边缘附近的数据不会被纳入合成数据（聚合区域29-32）。 时间平均处理分为月度和年度两种模式。版本1的月度合成图像尚未经过滤波以剔除极光、野火、船舶及其他瞬态光源产生的灯光。但年度合成图像则带有额外的分层处理流程，可移除瞬态光源与背景（非灯光）数值。 版本1的产品覆盖全球北纬75度至南纬65度的区域，采用15角秒的地理网格进行生产，以GeoTIFF格式封装为6幅瓦片。这些瓦片以赤道为界进行裁切，每幅瓦片覆盖120度纬度范围。每幅瓦片实际包含两组图像：分别为平均辐射度数值与有效观测次数。 在月度合成图像中，全球诸多区域可能因当月无法获取高质量数据覆盖——这可能是由于热带区域的云覆盖，或是极地在各自夏季出现的太阳光照所致。因此，数据集使用者务必参考无云观测文件，切勿默认平均辐射度图像中的零值代表未观测到任何灯光。 版本1的月度数据集采用两种不同配置进行全球处理：第一种会排除所有受杂散光影响的数据；第二种则会纳入经过杂散光校正流程的辐射度数据（参考文献）。这两种配置分别在文件名中以“vcm”与“vcmsl”标识。包含经杂散光校正数据的“vcmsl”版本在极地区域的数据覆盖范围更广，但数据质量有所下降。使用者需根据自身应用场景选择最合适的数据集。年度合成图像仅采用“vcm”配置进行生产，即排除所有受杂散光影响的数据。 文件名命名规则： 版本1的合成产品文件名包含7个由下划线“_”分隔的字段，每个字段内部可额外使用短横线“-”作为分隔符。文件名末尾附带扩展名。以下面的示例文件名为例进行说明： SVDNB_npp_20140501-20140531_global_vcmcfg_v10_c201502061154.avg_rade9 字段1：用于制作合成图像的VIIRS SDR或产品标识“SVDNB” 字段2：卫星名称“npp” 字段3：日期范围“20140501-20140531” 字段4：研究区域“global”（全球） 字段5：配置简称“vcmcfg” 字段6：版本号，“v10”代表版本1.0 字段7：创建日期/时间 扩展名：avg_rade9 年度产品的配置简称（字段5）可包含其他取值，具体如下： “vcm-orm”（VIIRS云掩膜-异常值剔除）：该产品包含经过异常值剔除流程处理的无云平均辐射度数值，可过滤野火及其他瞬态灯光。 “vcm-orm-ntl”（VIIRS云掩膜-异常值剔除-夜间灯光）：该产品基于“vcm-orm”的平均结果，将背景（非灯光）数值设为零。 “vcm-ntl”（VIIRS云掩膜-夜间灯光）：该产品基于“vcm”的平均结果，将背景（非灯光）数值设为零。 数据类型与格式： 为覆盖最广泛的用户群体，数据以压缩tar包形式分发，每个压缩包包含两幅GeoTIFF图像。扩展名为“avg_rade9”的文件存储浮点型辐射度数值，单位为纳瓦/厘米²/球面度（nanoWatts/cm²/sr）。请注意，原始DNB辐射度数值已被乘以1E9，此举旨在解决部分软件包无法处理原始单位下极小数值的问题。扩展名为“cf_cvg”的文件存储整数型计数，代表用于构建平均辐射度图像的无云覆盖次数（即有效观测次数）。扩展名为“cvg”的文件存储整数型计数，代表所有可用的覆盖次数（无论是否受云覆盖影响），即总观测次数。 引用说明： 使用该数据集时，请将产品生成方标注为地球观测小组、佩恩公共政策研究所（Payne Institute for Public Policy）。