1. What is the Normalized Difference Vegetation Index ?
Normalized Difference Vegetation Index (NDVI) is an important index to measure the greenness (biomass) of surface vegetation, which reflects the absorption of solar radiation by vegetation and the intensity of photosynthesis. The index is calculated from near-infrared and visible light reflected by the ground. It is worth noting that the value range of NDVI is generally between -1 and 1, and the closer the value is to 1, the higher the vegetation coverage and the greater the biomass.
The dataset presented this time was generated by the Aqua/Terra-MODIS satellite sensor MOD13Q1 product, a product that provides global surface albedo and vegetation indices every 16 days. This product is used to generate the monthly vegetation index product in your dataset.
The following is a brief description of the process of generating this dataset:
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Preliminary reconstruction of noise pixels of the same type of features : in this step, classify the same type of features (such as forests, grasslands, farmland, etc.) and eliminate the noise caused by meteorological conditions (such as clouds, fog, smoke, etc.) In order to obtain more accurate ground object reflection information.
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Long-term image SG filtering : SG filtering (Savitzky-Golay filtering) is a filtering method used to smooth noise and preserve edge characteristics. In this step, the long-term trend of vegetation change can be extracted by SG filtering on the long-time series of NDVI data while filtering out seasonal and random noise.
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Keep high-quality pixels : In this step, select high-quality pixels (less cloud occlusion, good viewing angle, etc.) to ensure the quality of the obtained monthly vegetation index products.
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16-day synthetic monthly product : Since the MOD13Q1 product is generated every 16 days, it is necessary to synthesize two or three 16-day products into one monthly product. The synthesis method adopts the monthly maximum value synthesis, that is, in each month, the pixel with the largest NDVI value is selected as the monthly NDVI value of the pixel.
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China-wide splicing : Finally, all monthly vegetation index products are spliced according to geographic location to generate NDVI products within China.
The application value of this data set is mainly reflected in the following aspects:
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Ecological quality assessment : Through long-term NDVI data, the long-term trend and seasonal changes of vegetation growth can be understood, so as to evaluate the ecological quality and sustainability of an area.
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Ecological space survey and assessment : NDVI data can reflect vegetation coverage and biomass, thus providing important information for ecological space survey and planning. For example, forest coverage can be assessed based on NDVI data to guide forest protection and management.
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Agricultural management : NDVI data can also be used in agricultural management, such as monitoring crop growth, predicting food production, and evaluating the impact of disasters (such as drought, pests, etc.) on agriculture.
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Climate change research : long-term NDVI data can reflect the impact of climate change on vegetation growth, thus providing important data for climate change research
2. Dataset introduction
This data set is a monthly normalized difference vegetation index product from 2000 to 2022 in China, with a spatial resolution of 250 meters. The synthesis method is based on the monthly maximum value. There are 12 periods per year, with a total of 275 periods. This product is based on the MOD13Q1 product of the Aqua/Terra-MODIS satellite sensor and land use data. After preliminary reconstruction of similar ground and noise pixels in single-phase images, SG filtering of long-term images, high-quality pixels are retained, and 16-day synthetic monthly products and Process generation such as China range splicing. This data set can provide data reference for national regional ecological quality evaluation, important ecological space survey and evaluation, etc.
Time Resolution: Months
Spatial resolution: 100m - 1km
3. Naming and usage of data files
File name: HXPT_NDVI_MONTH_MAX_250m_YYYYMM_National_yyyymmddhhmmss.tif, where HXPT stands for National Ecological Protection Red Line Supervision Platform Production, NDVI stands for Normalized Difference Vegetation Index, MONTH stands for monthly, MAX stands for maximum synthesis, 250m stands for spatial resolution of 250 meters, national representative Covering the whole country, YYYYMM represents the data time year and month, yyyymmddhhmmss represents the data production time year, month, day, hour, minute and second Data reading method: the file is stored in .tif format and can be opened by software such as ArcGIS.
Data address: https://www.dilitanxianjia.com/%e9%81%a5%e6%84%9f%e8%a7%a3%e8%af%91%e5%90%8e%e6%88%90% e6%9e%9c%e6%95%b0%e6%8d%ae/%e9%81%a5%e6%84%9f%e6%8c%87%e6%95%b0%e4%ba%a7%e5 %93%81/%e5%bd%92%e4%b8%80%e5%8c%96%e6%a4%8d%e8%a2%ab%e6%8c%87%e6%95%b0%ef% bc%88ndvi%ef%bc%89/