IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Research article
erd

Effects of Surveying Methods between GNSS and Direct
Leveling on Elevation Values over Long Distance inMountainous Area
TAKAHIKO KUBODERA*
Faculty of Science and Engineering, Toyo University, Saitama, Japan
Email: kubodera@toyo.jp

HIROMU OKAZAWA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, JapanYOSHIHARU HOSOKAWA
Emeritus Professor, University of Miyazaki, Miyazaki, JapanFUTOSHI KAWANA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan

EIJI MATSUO
Faculty of Engineering, Kyushu Sangyo University, Fukuoka, Japan

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Received 19 December 2015

Accepted 11 April 2016(*Corresponding Author)

Abstract Water use facilities such as irrigation and drainage channels, water gate, hydraulicdrop etc. are constructed to make water supply to paddy field and upland field. In a planning ofirrigation project, it is necessary to obtain elevation value with accuracy and efficiency aroundproject site. In generally, elevation values are obtained by the direct leveling survey withspecific instruments, e.g. digital or auto level, a couple of staffs and turning plates. The directleveling survey also needs several benchmarks, which are points of reference with highaccuracy location information including latitude, longitude and elevation. There is, however, aserious problem that survey work of the direct leveling survey must begin at several
benchmarks. In the case of survey work in mountainous area, surveyors must carry out thedirect leveling survey over several very-long routes, because there are few benchmarks. On theother hand, in the Global Navigation Satellite System (GNSS) surveying, elevation values canbe obtained indirectly by observing carrier phase from multi positioning satellites such as GPS,GLONASS since 2011. This study started to install the new benchmark on a 920 m highmountain, about 5 km away from some known benchmarks in Karuizawa Town, Nagano
Prefecture. After surveying the new benchmark by the GNSS and the direct leveling, we
compared its elevation values. Furthermore, a streamlined survey process, the influence onmost probable value and standard deviation by the difference of using satellite, “GPS-only” and“GPS and GLONASS” were investigated in the GNSS surveying. As the results, our tests foundthat dramatically streamlined survey process, “GPS-only” can obtain an elevation value that is
consistent with the value from the direct leveling survey. Therefore, the GNSS surveying isuseful to obtain accurate elevation values over long distance like very long channels.
Keywords GPS, GLONASS, rigorous network adjustment, observation durationⒸ ISERD

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INTRODUCTION
In agricultural irrigation projects, channels are planned to distribute water to the upland and paddy
fields within the project area. The channels in such project areas tend to be long. For distributing waterin long channels, it is important to use surveying technologies that clarify the elevations of planned
channel locations. Conventional survey techniques are time- and labor-intensive. Therefore, thedevelopment of survey techniques that are accurate and efficient has been promoted.
It is difficult for developing countries to prepare expensive surveying equipment and use highly
advance surveying systems. Such countries request that advanced nations provide them assistance on
surveying techniques. Japan once conducted a questionnaire survey on the GNSS continuous
observation system in countries receiving overseas development assistance from Japan (Nakagawa elal., 2014). The GNSS continuous observation system uses GNSS-based control stations (i.e.,observation stations with GNSS antennas and receivers) for data acquisition, and the system includes
analysis and provision of the obtained data. The survey showed that 16 of the 23 countries surveyed
had already introduced the GNSS continuous observation system (Nakagawa et al., 2014). Nine ofthose 16 countries reported using the system for agricultural purposes (Nakagawa et al., 2014). Judging
from the questionnaire results, the use of surveying techniques using GNSS in agriculture is being
promoted internationally. It is predicted that surveying using the GNSS continuous observation system
will become the mainstream technique. The introduction of the GNSS continuous observation system
can be expected to drastically eliminate the technical gap between developing countries and developed
countries.
In conventional direct leveling, whereby the elevations of planned locations for channels are
determined, the relative height are directly surveyed by using level, vertical leveling staffs and turning
plates (Okazawa et al., 2014). Observations are made by repeatedly placing the level and the levelingstaff at certain intervals along the route from the benchmark to the new point (Okazawa et al., 2014).
The problem with this method is that considerable work is required to conduct leveling of a route forplanned water channels if the route is in a mountainous area without any benchmarks nearby. The data
used in this method are a series obtained in the observations from the benchmark to the new point;
therefore, observation errors occurring between the benchmark and the new point greatly affect the
final results. Even one error in the routes is not permissible, and the responsibility of the surveyor isalways great. There are other problems, such as difficulties in determining what routes to use to accessthe survey points and the problem of traffic density and traffic safety at the survey points.
In GNSS surveying, which started to be used in 2011, the phases of carrier waves from GPS andGLONASS positioning satellites are observed. All that's required is for the GNSS equipment to be set
at the new point. Three-dimensional coordinates of the new point are determined by obtaining thebaseline vector from the GNSS-based control station to the new point. A geoid model is necessary for
determining the elevation, because the datum of GNSS surveying is a reference ellipsoid and the datum
for the elevation is the geoid. In Japan, Japan geoid model “GSIGEO2011”, which is a high-accuracy
geoid model, was created (Kodama et al., 2014). The new geoid model has made GNSS levelingpossible. GPS and GLONASS are separate systems and the observed data are different. Use of GPSonly or GPS and GLONASS is stipulated for public surveying in Japan. Use of GLONASS-only is not
authorized. Studies have compared the use of GPS to the use of GLONASS (Ikeda and Sada, 2012;
Mylnikova et al., 2015; Yasyukevich et al., 2015).
Based on such circumstances in Japan, GPS-only and combination of GPS and GLONASS wereused in this study. The areas where GNSS leveling is done for agricultural channel planning tend to be
far from the existing benchmark. Therefore, the authors selected a location for a new point at theelevation of about 920 m in a mountainous area. The new point was surrounded by large areas of
paddy fields and of upland fields for cabbage and blueberry cultivation. Even though the target area
already had irrigation channels, the local farmers requested that the accurate elevation of the area bedetermined.
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To examine the conformity of the elevation values surveyed by GNSS leveling and thosesurveyed by direct leveling, both techniques were used in observing the new point. The most probablevalue and the standard deviation of the elevation obtained by each technique were determined byrigorous network adjustment and were compared. In GNSS leveling, the influence of the difference
between GPS-only observation and GPS and GLONASS observation on the most probable value andthe standard deviation was clarified. To investigate the improvements in observation efficiency
achieved by GNSS leveling, the work volume of observation by GNSS leveling and by direct levelingwere determined and compared.
METHODOLOGY
Methodology of GNSS Leveling
The new point location was set near a paddy field area in a mountainous area at an elevation of about
920 m and about 5 km from the first-order benchmark in Karuizawa Town, Nagano Prefecture. Table 1
shows the outline of the GNSS leveling and direct leveling done for this study.
Table 1 Outline of the GNSS leveling and direct leveling done for this study
Used known point

Used satellite

Date

GNSS levelingNumber of
new point
1

3 GNSS-based control stations

GPS, GLONASS

23.Sep.2014

Direct leveling1

3 first-order benchmarks

None19-20.Sep.2013

MethodThe observation technique used in GNSS leveling was static relative positioning with carrier phaseobservable. Because the static is most accurate method in GNSS surveying such as the fast static, RTK
and so on. The GNSS leveling equipment used was Trimble R8 GNSS of Nikon Trimble Co., Ltd. (Fig.
1). The geoid model used was Japan geoid model “GSIGEO2011”. The map of network plan for GNSS
leveling was the Y-shaped connected traverse (Fig. 2). The GNSS-based control stations used in the
GNSS leveling were the three points No.960610, No.950269 and No.960613. The new point is denoted
as No.4101. No.4101 is denominated by the author to distinguish it from other points. Fig. 3 shows the
GNSS-based control station No.950269. The provision of GLONASS data, in addition to GPS data, wasstarted in 2013. This study used GPS-only, GPS and GLONASS data from GNSS-based control stations.
Coordinate value

Antenna height

New point 4101

Fig. 1 GNSS leveling survey

Fig. 2 Map of network planfor GNSS levelingⒸ ISERD

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Fig. 3 GNSS-based control
station No.950269

IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Methodology of Direct Leveling
The direct leveling was done to compare with GNSS leveling. Because the direct leveling is mostaccurate method in leveling survey. The equipment used for direct leveling was digital levels and barcode leveling staffs of Leica Geosystems Co., Ltd. or Topcon Corp (Fig. 4). The digital level isaccurate than auto level when reading the staff. Even though different levels used because surveyed atsame time on different routes, there are no different results comparing Leica and Topcon level. Fig. 5
shows the map of network plan for direct leveling. The first-order benchmarks used in direct levelingwere the three points No.18050 (Elevation 948.8876 m), No.18049 (Elevation 938.1914 m) andNo.546 (Elevation 940.1693 m). Three intersection points No.1, No.2 and No.3 were set for examining
each section. The new point is denoted as No.4101. Fig. 6 shows the first-order benchmark No.546.
The first-order benchmark is the benchmark with the highest accuracy. The elevation is marked in unitsof 0.1 mm.
Bar-code staff
Digital levelFig.4 Direct leveling survey

BenchmarkFig. 5 Map of network plan for direct levelingFig. 6 First-order benchmark No.546
Results of Work Volume of GNSS Leveling and Direct Leveling
Table 2 shows the work volume for GNSS leveling and that for direct leveling. GNSS leveling wasdone by one person (the author). The observation hours in GNSS leveling were 5 continuous hours.
The survey manual for elevation surveying by GNSS leveling specifies that the observation hours for
GNSS leveling shall be at least 5 continuous hours (Geospatial Information Authority of Japan. 2015).
Direct leveling was done by 24 people, including the author. The 23 people, excluding the author, weredivided into 6 groups of 3 or 4 persons to survey within 2 days. The observation hours for directleveling was 11 hours in 2 days. The total observation duration is the observation hours multiplied by
the number of observation persons. The total observation duration for GNSS leveling were 5 hours,Ⓒ ISERD

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and those for direct leveling were 264 hours. The total observation duration in GNSS leveling wereabout one-fiftieth (1/50) that of direct leveling. Even though the result varies depending on the lengthof the route for direct leveling, the examination clarified that GNSS leveling is able to dramatically
improve observation efficiency. Based on the experience of conducting both leveling methods, theauthor is able to conclude that the use of GNSS leveling helped overcome many problems regarding
direct leveling, including planning for routes to the survey points, problems of traffic conditions andtraffic safety at the survey points, and the mental stress on the surveyor in work that does not allow
even one error.
Table 2 Work volume for GNSS leveling and that for direct leveling

GNSS leveling survey

Number ofobservation persons
1

Observation
hours [h]5Total observation
duration [h]5Direct leveling survey

24

11

264

MethodRigorous Network Adjustment
To determine the most probable value and standard deviation of the elevation of the new point basedon the observed data (i.e., the relative height or baseline vectors), rigorous network adjustment wasdone for the data obtained by GNSS leveling and direct leveling. In rigorous network adjustment, anobservation equation and a residual equation are formulated for the unknowns of the new point, anormal equation is formulated by using the least-squares method and that equation is solved (e.g.
Tajima and Komaki, 2001).
Eq. (1) is the formulated observation equation.
(1)

AX L

Where

A : Coefficient matrix
X : Unknown vector
L : Constant vector

The unknown vector is the unknown to be determined, and the constant vector includes theobserved values and the values for the known points. Practically, each observed values contains error.
Therefore, a residual equation shown as Eq. (2) is formulated.
V(2)

AX  LWhere
V : Residual vector
Then, a normal equation is formulated based on the least-squares method such that the sum ofsquares of the residual vector V T PV for which the weight is considered is the smallest. Eq. (3) is theformulated normal equation. The weight is a function of distance.
A T PAX(3)

A T PLWhere
P : Weight matrix
Eq. (4) shows the solution for the normal equation, and Eq. (5) shows the residual. To fulfill therequirement for high accuracy, the unknown is determined by using the observed value, which isgreater than the unknown, and the least-squares method. The most probable value of the unknown,
which is the most probable value for the elevation of the new point, is determined as a solution Eq. (4)to the normal equation obtained by using the least-squares method.
ˆX

A T PA

1(4)

A T PLⒸ ISERD

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Where
ˆ
V

X̂ : Solution of the normal equation obtained by using the least-squares method.

ˆ L
AX

A A T PA

1

(5)

A T PL  L

WhereV̂ : Residual of the normal equation obtained by using the least-squares method.
Eq. (6) shows the standard deviation of unit weight. The standard deviation of unit weight is thestandard deviation of the observed weight.
ˆ T PV
ˆ
V
nm

m0

Where

(6)

m0 : Standard deviation of unit weightn : Number of the observation equations
m : Number of the unknowns

The inverse matrix of the coefficient matrix of the normal equation is shown as Eq. (7), which iscalled the weight coefficient matrix.
Q

A T PA

(7)

1

Where
Q : Inverse matrix of the coefficient matrix of the normal equation
Eq. (8) shows the standard deviation of the most probable value of the unknown. This standard
deviation is the standard deviation of the most probable value of the elevation of the new point.

mi

(8)

m0 qiiWheremi : Standard deviation of the most probable value of the unknownqii : Diagonal line element of Q

However, rigorous network adjustment uses matrices to determine the many unknowns; therefore,
computer applications are used in actual situations. Rigorous network adjustment for GNSS levelingwas done by using TOWISE 4.1.1 (Japanese version) of Nikon Trimble Co., Ltd. and that for directleveling was done by using BLUETREND XA (Japanese version) of FukuiComputer, Inc.
RESULTS AND DISCUSSION
Generally, the accuracy of the most probable value is evaluated by the standard deviation. The
probability, the observed value vary within the standard deviation around the most probable value, isknown as 68.3 %. The most probable value and standard deviation of the elevation of the new point
No.4101 determined through rigorous network adjustment using the values obtained by GNSS levelingand those obtained by direct leveling are shown in Table 3. The most probable value determined by
GNSS leveling using GPS-only was 919.928 m. That determined by GNSS leveling using GPS andGLONASS was 919.946 m. That determined by direct leveling was 919.921 m. The standard deviationof GNSS leveling using GPS-only was 0.018 m. That of GNSS leveling using GPS and GLONASS
was 0.021 m. That of direct leveling was 0.010 m. The standard deviation of direct leveling was thesmallest. That for GNSS leveling using GPS-only was the second smallest. That for GNSS levelingusing GPS and GLONASS was the third smallest.
The most probable value and standard deviation of the altitude of the new point No.4101
determined through rigorous network adjustment of the values observed by GNSS leveling, thoseobtained by direct leveling, and the discrepancy between the two values are shown in Table 4. The
discrepancy was obtained by subtracting the value observed by direct leveling from the value observedⒸ ISERD

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by GNSS leveling. The discrepancy between GNSS leveling using GPS-only and direct leveling was 7mm. The discrepancy between GNSS leveling using GPS and GLONASS and direct leveling was 25
mm. The results can be regarded as mutually consistent, even though the leveling techniques aredifferent. We can conclude that elevation with high accuracy, i.e., sufficiently consistent with theresults of direct leveling, was obtained by GNSS leveling using GPS-only. The reason for thediscrepancy between the results of GNSS leveling using GPS-only and the results of GNSS levelingusing GPS and GLONASS is thought to be that GPS and GLONASS are different systems. It isthought that GPS-only observation and analysis is better than GPS and GLONASS when and whereenough satellites are available for GPS-only operation.
Table 3 Most probable value and standard deviation of the elevation of the new point
MethodGNSS leveling survey
Direct leveling survey

GPS-only

Name ofnew point
4101

Most probablevalue [m]919.928

Standard
deviation [m]0.018

GPS+GLONASS

4101

919.946

0.021

None

4101

919.9210.010

Used satellite

Table 4 Discrepancy of elevations between GNSS leveling and direct levelingGPS-only

Name ofnew point
4101

Most probablevalue [m]+ 0.007

Standard
deviation [m]+0.008

GPS+GLONASS

4101+ 0.025+0.011

Used satellite
Discrepancy

CONCLUSIONAs the conclusions, the points are summarized in the following.
(1) The total observation duration in GNSS leveling were about one-fiftieth (1/50) that of directleveling. GNSS leveling is able to dramatically improve observation efficiency.
(2) The discrepancy between GNSS leveling using GPS-only and direct leveling was 7 mm. The
discrepancy between GNSS leveling using GPS and GLONASS and direct leveling was 25 mm. The
sufficiently consistent with the results of direct leveling was obtained by GNSS leveling using GPSonly.
(3) It is thought that GPS-only observation and analysis is better than GPS and GLONASS when andwhere enough satellites are available for GPS-only operation.
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