rice cultivation increases because it is a staple food, in
particular for the rapidly growing Asian population.
Casanova etal. (1998) already presented a study about
monitoring rice during the growing season with a hand-held
radiometer. Their conclusion was that only biomass can be
predicted with a high accuracy (R?—0.97). The possibility to
estimate the leaf area index (LAT) from spectral data is limited
(R?—0.67). Recent studies focus on deriving different vegetation
properties, like the LAI and the green leaf chlorophyll density
(GLCD), from remote sensing data. Therefore, Yang et al.
(2011) compared different transformations for reflectance data,
obtained from a spectroradiometer, concerning their capability
of predicting rice biophysical parameters. In another study
Ryuetal. (2011) used an airborne hyperspectral sensor to
determine the nitrogen content of rice plants at the heading
stage. In the context of rice growth monitoring, Koppe et al.
(2012) demonstrated the potential of multi-temporal and dual-
polarimetric TerraSAR-X data based on a survey carried out in
the same region observed in our study. However, any studies
about TLS measurements for rice exist at this stage.
Thus, we evaluate the applicability of multitemporal TLS for
rice growth monitoring in this approach. In contrast to other
presented studies using phase-shift or optical probe sensors, a
time-of-flight sensor was used. The surveys were carried out on
test sites related to the ICASD project. The International Center
for Agro-Informatics and Sustainable Development (ICASD)
was founded in 2009 as a cooperative research center between
the China Agricultural University, Beijing and the University of
Cologne, Germany (ICASD, 2012). Besides the development of
an open, international, and multidisciplinary platform for agro-
informatics and sustainable development, one of the major aims
is the application of information sciences and technologies in
the field of agriculture.
2. METHODS
2.1 Study area
We conducted our surveys on test fields close to the city
Jiansanjiang (N 47°13'54", E 132°38'53") in Heilongjiang
Province in the far northeast of China. The Province with a
continental monsoon climate is an important basis for
agricultural products (Gao & Liu, 2011).
The focus of the monitored field experiment was on different
nitrogen fertilizer inputs during the growing period. One half of
the paddy rice field with a spatial extent of 60 m by 60 m was
cultivated with the rice variety Kongyul31, the other one with
Longjing21. Furthermore, nine different treatments were
repeated thrice for both rice varieties. The treatments differ in
Figure 1. Overview of the investigated area from one scan position at the south edge of the field. On the right
with the tripod mounted on the small trailer can be seen.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
the amount of applied nitrogen fertilizer during the early and
middle growing period. Thus, the area was divided into 54 plots
(10 m by 7 m).
2.2 Surveys
For all field campaigns the terrestrial laser scanner Riegl
VZ-1000 (Riegl LMS GmbH, 2011), provided by Five Star
Electronic Technologies, located in Beijing, was used. The
narrow infrared laser beam with online full waveform analysis
and echo digitization enables the fast recording of high-accurate
3D point clouds. Additionally, a digital camera, Nikon D700,
was mounted on the laser scanner. From the recorded RGB-
photos the point clouds gained from the laser scanner can be
colorized and the corresponding surfaces can be textured.
The instrument was fixed on a tripod, which raises the sensor
up to 1.5 m above ground. Where possible, the whole setting
was build up on a small trailer behind a tractor to achieve a
greater height (cf. Figure 1). In order to capture the whole study
area, nine scan positions were established. For the analyses
presented in this paper, four of them were of major importance:
Two positions without the trailer at the north edge and two
positions with the trailer at the south edge of the investigated
field.
For the monitoring approach, three campaigns were carried out
on the 21* of June, the 4^, and the 18" of July 2011. The
chosen period is within the vegetative stage of the rice plants,
when the stem elongation process takes place. Remarkable
differences between the dates were assumed, due to the increase
of tillers and plant height during this stage.
Moreover, common tie points in all scans are required to enable
the merging of all scan positions in the postprocessing.
Therefore, high reflective cylinders that can be easily detected
by the laser scanner, were fixed on ranging poles build upon the
dikes between the fields (Hoffmeister et al, 2010). The
positions of these poles were marked with large nails in the first
campaign. Thus, every scan of each date can be merged together
by reestablishing the ranging poles for the other two campaigns.
Furthermore, on each date the plant heights of eight to ten
plants per plot were measured manually and plant samples were
taken to evaluate the biomass of stem and leafs.
2.3 Postprocessing
For the postprocessing of the achieved data, Riegls software
RiSCAN PRO, which is delivered with the laser scanner, was
used. The first registration and merging of the scan positions
was performed with an indirect registration method, based on
the mentioned high reflective cylinders acting as tie points.
EX
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side the scanner
