## 3 Core Sites and Preliminary Stations of the VRPC  
After a comprehensive study of local geographical and climatic features, ecosystem representatives, infrastructure and observation facilities, we plan to reform and construct approximately 12 observation fields distributed in seven areas in China as the core observation fields of the national remote sensing products validation network (Figure 2). During the first period of the project execution (2012-2014), we bring four remote sensing stations with the best infrastructure and observation facilities into the remote sensing national validation network as a pilot for collaborative networking experiments for satellite-airborne-ground synchronous observations and the validation of remote sensing products. For each station, several standard observation fields with dimensions of 3 km \(\times\)3 km will be established for remote sensing product validation. Because China is a mountainous country and the mountainous and hilly areas make up about 43% of the total area, the observation fields will have at least an area of 2 km \(\times\) 2 km in these regions with fragmented landscapes. Observation fields that are used for validating the soil moisture inverted by passive microwaves will have areas of 25 km \(\times\)25 km. For every standard observation field that is planned to be built, we have used the regional multi-resolution satellite images (e.g., Quickbird and TM) and ground survey (e.g., leaf area index, soil moisture, land surface temperature, land cover) to calculate the background values of the observed elements for the target area. The other background values will also be collected, such as digital elevation model data and soil property data. Furthermore, based on the above prior knowledge of the observation fields, we used the layout optimization approaches of the heterogeneous pixel scale from the first part of the project to design all elements of the ground observation systems in the experiment fields [21,22]. Subsequently, we deployed observation nodes and facilities. The observation systems will contain a multi-scale nested layout mode (_i.e._, the sensor network (with a 1\(\sim\)10 km scale)), a large-aperture scintillator (with a 1 km scale), eddy covariance (with a 100 m scale), ground-based remote sensing (with a 1 m scale), and _in situ_ point observations) to manage the validation of remote sensing products with various resolutions. According to the selection principles of the observation sites and the preliminary design of the core sites, four existing stations were selected for inclusion in the first stage of the VRPC. They are the Heihe Remote Sensing Experimental Research Station (Heihe Station), the Huailai Remote Sensing Test Station (Huailai Station), the Changchun Jingyuetan Remote Sensing Experimental Station (JingyuetanStation), and the Hulunber Grassland Ecosystem Observation and Research Station (Hulunber Station). The locations of these four stations are shown in Figure 2. Table 1 provides the summary information for each observation site of the three stations, including longitude, latitude, elevation, total annual precipitation, average annual temperature, land cover, LAI, and core scientific aims. The summary information for Heihe Station is shown in Table 2. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Station** & **Core Site** & **Location** & **Meteorology** & **Land Cover** & **Scientific Aims** \\
**Name** & **(Science Network)** & & & & \\ \hline \multirow{2}{*}{Hualiali} & East garden controlled & Prov.: Hebei; & & & \\  & experimental site (RSON) & Long.:115.783; & & & \\  & 100 m\(\times\)100 m & Lat.: 40.349; Ele.: 488 & & & \\ \hline \multirow{2}{*}{Hualiali} & East garden (RSON) & Prov.: Hebei; & & & \\  & Long.:115.783; & & & \\  & 1.5 km\(\times\)2 km & Lat.: 40.349; Ele.: 488 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Information on the core observation sites for the validation network for remote sensing products in China (VRPC). Figure 2: Core sites of the VRPC and their land cover types.