IEEE Geoscience and Remote Sensing Magazine - September 2020 - 24

NAQU SOIL OBSERVATORY AND A'LI SOIL
OBSERVATORY EXPERIMENTS
An array of base stations was established to collect the
primary variables necessary for product validation and
improvement.
MULTISCALE DEPLOYMENT
With 50 sites, the NSO and ASO were deployed over four
successive summers, from 2014 to 2017. The latitudes and
longitudes of all sites and background information are
shown in Tables 2 and 3, respectively. Different deployment
schemes were adopted by different land cover types in the
NSO and ASO (Figure 2). For the NSO, the land cover and
satellite pixel orientation required a nested, multiscale networking scheme in pure pixels. However, for the ASO, with
a more diverse landscape, the random networking scheme
was used.
The NSO experimental area [Figure 2(a)] is in the Qiangtang grassland and characterized by flat terrain, homogeneous grassland types, higher vegetation biomass, a gentle
SM dynamic range, and a typical freeze/thaw cycle. Deployment of the sites began in August 2014, and the full
set of 33 stations was completed by August 2015. The SM
and temperature are measured across four spatial scales in
the 2 pixel # 2 pixel arrangement. These scales are at 1, 5,
15, and 25 km. They extend to 75 km, with around five
pixels. These data can be organized for land surface estimates matching a variety of hydrological modeling and microwave products for different purposes. The 1- and 5-kmscale data can match the resolutions of polar-orbiting and
geostationary satellites, respectively. Currently, the 1- and
2-km-scale data are appropriate only for radar-based satellite products or aircraft/drone systems. A key feature of the
NSO is that the alignment of multiple satellite SM products
was considered to optimize nested intercomparisons between those products.
The ASO experimental area [Figure 2(b)] is in the A'li
area of the western TP and characterized by complex terrain, multiple land cover types (desertification grassland,
wetlands, and a small water body), and low vegetation
biomass. It has a limited SM dynamic range and a typical
freeze/thaw cycle. There was a total of 17 sites as of October
2016. The SM and temperature are measured at four spatial scales (3, 5, 10, and 25 km), with random deployment.
These data also match the different scales of land hydrological modeling and passive and active microwave products.
The 3-km-scale data are specifically developed to address
the active-passive resolutions of such missions as SMAP.
At the 33 NSO sites, in addition to soil temperature and
moisture measurements, many auxiliary parameters are
measured, including infrared radiation temperature, emissivity, soil texture, soil dielectric constant, vegetation coverage, and vegetation type. The soil texture and organic matter content in 0 to 5 cm of soil at each site are measured by a
laser particle-size analyzer and a total organic-carbon analyzer in the laboratory and are available in the observatory's
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metadata. These parameters can help to analyze the features of multiscale SM and temperature on the TP.
INSTRUMENT INSTALLATION AND DATA
TRANSMISSION
SM and temperature are measured at five soil depths. One
or two sensors are installed in the top layer, in 0-3 cm of
soil, inserted from the surface at a 45° angle. The other
sensors are inserted vertically at depths of 5, 10, 20, and
30 cm at each of the 33 stations. The installation is designed to match the sensing depths of most X-, C-, and Lband-based radiometers currently deployed, such as the
FY, SMOS, SMAP, and ASCAT instruments. The data are
recorded every 10-30 min, representing the prior 10-30min average.
For the data transmission, each data logger is mounted
in an enclosure box at a height of 1.5 m [Figure 3(a)], and
data records are sent via wireless transmission network.
To limit the damage to the installation from livestock and
wildlife and interference from the public, a 1.5-m steel
fence is installed around each site, which helps to provide a
long-term, continuous data record.
The wireless transmission system aims for real-time
remote monitoring of soil, vegetation, and meteorological changes distributed across the soil observatories. The
sensor nodes communicate with the base station through
wireless transmission techniques, i.e., general packet radio
service (GPRS). To solve the problem of field instrument
power supply in this cold area, a dual power-supply system
was designed that contains a solar panel system and three
parallel rechargeable battery systems [Figure 3(b)]. In the
daytime, the solar panel charges the batteries and supplies
power to the system. One of the three parallel rechargeable batteries works at night. Another five rechargeable
batteries in the EM50 logger can also support continuous
data measurement.
To ensure that the instrument can work normally in the
winter, the dual power-supply system is used, which can
channel some thermal energy to increase the surrounding
temperature of the data logger so the internal temperature
is maintained above 0 °C. The instrument status can be obtained through a cellular phone signal, including the status
of the solar circuit, battery power, signal strength, instrument temperature, instrument working state, GPS positioning, and so forth. Two software platforms (see the "Data
Management" section) for the wireless transmission system
were developed and are able to automatically transmit and
archive observed data and remotely access updates and
-alterations to the logger system, if necessary.
THE NAQU CLIMATE STATION
The NCS (Figure 4) is an automated climate and weather
station to conduct a temperature and humidity vertical
profile observation of a section from 30 cm underground
to 3.5 m aboveground, defined in this article as the soil-
atmosphere interface layer. This station provides valuable
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