Journal of Natural Disaster Science, Volume 31, Number 1, 2009, pp1-10

Estimation of ginkgo leaf necrosis induced by Typhoon 0613 with spectral reflectance
Wang FEI*
Haruhiko YAMAMOTO**
Yasuomi IBARAKI**
Kiyoshi IWAYA**
Naru TAKAYAMA***United Graduate School of Agriculture Science, Tottori University**Faulty of Agriculture, Yamaguchi University(Received for 9 Jan., 2008 and in revised from 7 Oct., 2008)
ABSTRACT
Typhoon No. 13 in 2006 (Typhoon 0613) passed through Yamaguchi Prefecture,
Japan on Sep. 17, 2006. After being hit by it, many landscape trees, especially ginkgo in
Yamaguchi City, showed symptoms of necrosis on the leaf tip and margin, and even theentire leaf. It clearly divided the crowns of some ginkgo trees into the green part and thenon-green part. In order to quantitatively study this phenomenon, the normalized difference
vegetation index (NDVI) near red edge for ginkgo leaves, measured by a pocket radiometerin the lab, was used to estimate leaf necrosis induced by Typhoon 0613. Based on thisresearch, the optimum wavelength for calculation of the NDVI value of ginkgo leaves
damaged by Typhoon 0613 is 679 and 755 nm, which sufficiently corresponds to variancein ginkgo leaf necrosis. By leaf necrosis investigation, the difference in the percentage ofnecrotic leaves between the windward and leeward sides made the crowns of damaged
ginkgo trees show different colors on either side of the crown. An inverse linear relationshipbetween the necrotic area percentage (NAP) and NDVI755nm/679nm was obtained for ginkgo
leaves. By analysis of the NDVI using ratio (NDVIr) value of crowns, it was indicated that
there were differences in leaf necrosis induced by Typhoon 0613 among sites of different
distances away from the coastline and between ginkgo and other tree species. It has
potential to be an alternative tool for evaluating the damage status of ginkgo trees hit bytyphoons like Typhoon 0613.
Keyword: Ginkgo, Leaf necrosis, Typhoon 0613, NDVI, Spectral reflectancedamage to trees and shrubs, for example, by uprooting, stem breaking, bending and leaning, and so on(Takahashi et al., 1981; Yamamoto, 1979; Nobel,
1981; Maki et al., 1991). They are also complex calamities that can induce many unfavorable extreme
conditions like flooding, gusty winds, and drought aswell as salt/sand spray, which cause plants physiological injury (Maki et al., 1991; Nobel, 1981). Ginkgo(Ginkgo biloba L.) is a showy landscape tree species,

1. Introduction
Many plants show symptoms of necrosis at theleaf tip and margin when they are affected by extreme
environmental conditions such as salt toxicity, water
stress, high/low temperature, nutrition deficiency,
injured root and trunk, transplanting shock, and disease (Treshow, 1970; Durbin, 1978). Typhoons are
one kind of disaster that can cause serious mechanical
1

WANG FEI, H. YAMAMOTO, Y IBARAKI, K. IWAYA, N. TAKAYAMA

which is widely planted in China, Japan, and so on.
However, it often shows leaf necrosis (Okinaka et al.,1990) and branch dieback (Shimizu, 2004) after damage by high temperature (Treshow, 1970) or by strong
dry typhoon, especially along the coast.
Typhoon 0613 was characterized by low precipitation and high wind speed with maximum gusty
wind speed of 42.4 m/s, maximum wind speed of 20
m/s, and precipitation of 26 mm when it hit Yamaguchi City. However, during the hit, as the maximum
wind speed reached its peak value, there was almost
no rainfall. This rainless or less-rain period persisted
more than one month after the hit. Following Typhoon
0613, it is observed that leaf necrotic symptoms appeared on many landscape trees and shrubs in Yamaguchi City, particularly ginkgo. It made the crownsof ginkgo trees obviously different between thewindward and leeward sides, which became a problem to be studied in this paper. This kind of damage
has also been reported in other papers. Ginkgo trees
with symptoms of leaf necrosis extended inland evenas far as 100 km from the coastline during the hit by
Typhoon 8218 in the area of the Kanto plain, Japan(Okinaka et al., 1984). However, the visual scale
method was more common in research on ginkgo
crowns damaged by typhoons. In this paper, spectralreflectance was used to estimate the damage status inorder to find an objective method of estimation andevaluation.
As an important non-destructive approach, thenear-infrared spectral analysis method has been widely utilized in the area of agriculture and medicine andthe food, fiber, and chemistry industries. In the fieldof agriculture, it was originally used for the things
with lower water content, and its application in fruits,
vegetables, and crops with higher water content began
in modern times (Iwamoto et al., 1994). However,spectral reflectance measurement has been used toestimate the plant leaf area index (Yamamoto, 1998),
chlorophyll concentration (Carter et al., 1994, 2001;
Ito et al., 2003), nutrient elements (Hinzman et al.,1986), water content (Yamamoto et al., 1995; Carter
et al., 1993; Ito et al., 2003), and so on. Carter et al.
(1994) considered that spectral reflectance in narrow
wavebands within the 690- to 700-nm range and its
ratio to near-infrared reflectance should provide earlier detection of stress-induced chlorosis comparedwith broad-band systems or narrow bands located atlesser wavelengths. Ito et al. (2003) diagnosed thechlorophyll content by the ratio of spectral reflectanceat 800 nm and 680 nm. Under water stress, and thechange of plant spectral reflectance in the near-infrared range has been reported in some other researches(Holben et al., 1983; Jackson et al. 1985; Moran etal., 1989; Yamamoto et al., 1995; Penuelas et al.,1999). Thorhaug et al. (2006) stated that browningand necrosis resulted in a clear change in the shape ofthe reflectance spectra of Thalassia blades and suggested that the reflectance spectra at 750 nm might
be a suitable stress index. Riedell et al. (1995) notedthat crop canopy chlorosis and necrosis in small grain
fields infested with greenbugs, etc. could be used asa diagnostic tool to detect crop damage from cereal
aphid population outbreaks. Yamamoto et al. (1996)
reported that it was possible to detect the leaf area ofsoybean damaged by the common cutworm with thenormalized difference vegetation index (NDVI) at
750/600 nm. Steddom et al. (2005) reached the conclusion that the use of radiometric methods has thepotential to increase the precision of assessment of
Cercospora leaf spot foliar symptoms of sugar beet
while eliminating potential bias.
Nevertheless, whether or not it can be used inestimating the damage status of landscape trees hit
by strong typhoons like Typhoon 0613 still needs tobe researched. What is the optimum wavelength forevaluating the damage status and are there any differences among tree species and trees planted at different
sites of different distances from the coastline? In thisstudy, after selecting the optimum spectral reflectancewavelength, leaf necrosis of ginkgo trees induced by
Typhoon 0613 was estimated by spectral reflectanceanalysis combined with the visual scale method. Bymeasuring the necrotic area percentage (NAP) andNDVI of necrotic leaves, the relation between themand the difference in the spectral reflectance of ginkgo leaves among different sites and between ginkgo
and other tree species were studied.
2. Materials and Methods
In this research, three experiments were carriedout. The first was to study the percentage of differently necrotic leaves in the crowns of ginkgo trees.
The second was to study the difference in spectral reflectance between ginkgo and other tree species after
2

ESTIMATION OF GINKGO LEAF NECROSIS INDUCED BY TYPHOON 0613 WITH SPECTRAL REFLECTANCE(NDVIr) values in the paper were calculated by thespectral reflectance value at these two wavelengths
except the NDVI value in the optimum wavelength
analysis.

being hit by Typhoon 0613. The third was to study thedifference in ginkgo leaf necrosis among three sites ofdifferent distances from the coastline.
2.1 Measurement of leaf necrotic percentage
and spectral reflectance
To study the percentage of necrotic leaves in thecrowns of ginkgo trees, six standard branches, three
from the leeward side and three from the windwardside, from three trees in a shelterbelt were sampledfrom Yamaguchi University. All the leaves on the
branches were visually divided into five necrotic levels according to the necrotic area percentage.
After counting the leaf number, the spectralreflectance for leaves of each level was measured
respectively by a radiometer, EKO-MS720, made by
EKO Instruments Co. Ltd. Its spectral resolution is 10
nm, its interval of wavelength is 3.3 nm, and the specified wavelength ranges from 350 to 1050 nm. Leaves
were measured with a special method in an indoor environment in order to avoid the effect of the gap fraction (Ito et al., 1996) and light condition between thewindward and leeward sides of trees in the field measurement, because it is not easy to obtain comparable
spectral reflectance data for trees under these conditions. The radiometer was mounted on a tripod 30 cm
above the sample leaves. A tray of 20×30×4 cm andvertically measured under a 40-w incandescent lamp
was smoothly filled with the sample leaves. A field ofview of 25° was selected and the area coverage was
139 cm2, approximately equal to a circular area with adiameter of 14 cm. Measurements were controlled bya piece of white paper corrected by a standard whiteboard of barium chloride, and three duplications foreach level were conducted at different positions on
the tray. The spectral reflectance was used to calculate
the NDVI by Equation (1):NDVIm / n NIRm VIBn
NIRm VIBn

2.2 Measurement of NAP
The leaves were scanned with a Canon D125u2
scanner, and the NAP of each leaf was calculated by
the image pixel method. NAP is the proportion of necrotic area to overall leaf area. It was determined byobtaining pixels of the overall leaf and then separating the green part (refer to Fig. 1) from the leaf withthe eraser tool of Photoshop. The NAP was calculated
by Equation (2), and the NAP value for the level ofeach leaf was the average NAP value of every leaf on
the related scale.

NAP  100 (Pixels for green areas 100 )
Pixels for overall leaf

(2)

Fig. 1 Overall leaf and green part of a necrotic leaf

2.3 Measurement for comparison between
ginkgo and other tree species
The tree species used for comparison with ginkgo include metasequoia (Metasequoia glyptostroboides Hu et Cheng), trident maple (Acer BuergerianumMiq.), and kaizuka juniper (Sabina chinensibs L.),
which are widely planted in Yamaguchi City. Leaves
were mechanically sampled from shelterbelts ofginkgo, metasequoia, and kaizuka juniper, and froman individual trident maple tree in Yamaguchi University. The spectral reflectance for leaves of every
species was measured by the method mentioned in 2.1
with four duplications for each species. The averageof the four duplications of spectral reflectance wasused to calculate the NDVI value by Equation (1).
The NDVIr is an average value between the NDVI
value for leaves on the windward side and the NDVI
value for leaves on the leeward side. It was calculated(1)

where NIR m is the spectral reflectance in thenear-infrared region, VIBn is the spectral reflectancein the visible region, m = 750, 760, ……, 900, and n= 630, 640,……, 690. According to the wavelength
analysis, the optimum wavelength for calculating the
NDVI was 755 nm and 679 nm for NIR and VIB.
Therefore, all NDVI values and NDVI using ratio
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WANG FEI, H. YAMAMOTO, Y IBARAKI, K. IWAYA, N. TAKAYAMA

with three duplications for each site. The average ofthe three duplications of spectral reflectance was used
to calculate the NDVI value by Equation (1). The
NDVIr values were also calculated by Equation (3).

as Equation (3).

NDVIR NDVI for leaves on windward NDVI for leaves on leeward
s100
2

(3)

2.4 Measurement for comparison among three sites
To study the difference in leaf necrosis amongsites of different distances from the coastline, Site A,
Site B, and Site C were selected. Site A is located at
Tokusa in Anno Canyon, Site B, at Yamaguchi besides
the Fusino River, and Site C, at Ube near Yamaguchi
Bay, which are 40.1, 12.6, and 1.7 km away from thecoastline, respectively. Sampling and measurement
were carried out on Nov. 1 and Nov. 2, 2006 for Site
A and Site B and on Nov. 6 and Nov. 8, 2006 for Site
C. The distance from the coastline (DC) is the shortest distance from any of the three sites to the coastline
measured by an electronic atlas tool named Atlas Z
Proffessional5. Meteorological data for these threesites were obtained from the Automated Meteorological Data Acquisition System of Japan.
Six standard branches, three from the windward side and three from the leeward side, were also
sampled for each of the three sites, respectively. The
method of leaf counting was the same as the abovementioned scale method.
The spectral reflectance for leaves of every site
was also measured by the method mentioned in 2.1

3. Results and discussion
3.1 Selection of the optimal spectra wavelength
for the measurement of ginkgo leaves
After summarizing a number of studies concerned with responses to physiological stress, Carter
et al. (2001) considered the maximum difference inreflectance within a 400- to 850-nm wavelength range
between control and stressed states occurring at wavelengths near 700 nm. Spectral reflectance is affectedby strong chlorophyll absorption in the range of 670–
680 nm and changes with variation in leaf anatomy
or water content in response to stresses beyond 730
nm in the near-infrared region (Carter et al., 2001).
Slaton et al. (2001) considered that leaf reflectance inthe near-infrared region is primarily affected by leaf
structure and the position of the red edge correlatedwith chlorophyll content, plant phenological stage, as
well as plant stresses. Leaf necrosis is characterized
by chlorophyll loss and leaf drying as well as leaf
structure variation. The optimal wavelength should
exist in these regions.
According to the definition of NDVI, many

Fig. 2 Variance in NDVI value for ginkgo leaves with different necrotic levels in the visible band (Figure 2-a)and near-inferred band (Figure 2-b). All of the NDVI values in Figure 2-a were calculated by every spectralreflectance value in the visible region and one definite spectral reflectance value from the near-infrared region
at a wavelength of 755 nm. All of the NDVI values in Figure 2-b were calculated by every spectral reflectancevalue from the near-infrared region and one definite spectral reflectance value in the visible region at awavelength of 679 nm. From this figure, it is evident that the maximum variance in NDVI value is located at awavelength of 679 nm and 755 nm, and the same values are maintained when they are calculated by different
definite spectral reflectance values.
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ESTIMATION OF GINKGO LEAF NECROSIS INDUCED BY TYPHOON 0613 WITH SPECTRAL REFLECTANCE

variance in necrosis of ginkgo leaves and a significant
difference between the windward and leeward sides
after Typhoon 0613 hit were observed (refer to Fig.
3). From Figure 3, it can be seen that most leaves leeward of the sampled crowns are non-necrotic leaves,
overall green leaves account for 70.9%, and no leaves
have become entirely brown. Most leaves windwardof the sampled crowns are necrotic leaves and driedleaves, and only 7.83% of them were green overall.
This means that it was the difference in the percentage of necrotic leaves between the windward andleeward sides that made the crowns of the damaged
ginkgo trees show different colors on either side of
the crown.
Many previous researches on typhoon damage to trees have involved ginkgo (Okinaka et al.,1984, 1990; Shimizu, 2004). However, researches on
ginkgo seldom focus on spectral reflectance characteristics. The visual scale method has been more commonly used to observe the damage characteristics ofcrowns (Okinaka et al., 1984, 1990; Shimizu, 2004;
Muhammed et al., 2003), and few of them have been
involved in the quantitative study of leaf necrotic area
percentage. In this study, the results of spectral reflectance for different necrotic levels of ginkgo leaves
showed a great difference, indicating an inverse liner
relationship between NAP and NDVI755nm/679nm, where
R 2=0.985 as shown in Figure 4. It means that the
NDVI value decreases as the leaf necrotic area increases. The NDVI values corresponded well with theginkgo leaf necrotic area. Evidently, it is possible toestimate the necrotic area by measuring the spectralreflectance of leaves.

NDVI values can be calculated by measuring spectralreflectance. In this research, the proper wavelength
for calculation of NDVI was determined by maximum variance of NDVI for ginkgo leaves of different
necrotic levels. Ginkgo leaves for selecting the optimal spectra wavelength were sampled from a ginkgo
shelterbelt in Yamaguchi University. After measuring
the spectral reflectance in the visible region and nearinfrared region, the NDVI values for all of the wavelengths from 600 to 900 nm were calculated. For thevisible region, all the NDVI values were calculated
by every spectral reflectance value in the visible region and one definite spectral reflectance value fromthe near-infrared region at a wavelength of 755 nm(refer to Fig. 2-a). For the near-infrared region, all
the NDVI values were calculated by every spectralreflectance value from the near-infrared region and
one definite spectral reflectance value in the visible
region at a wavelength of 679 nm, comparatively (refer to Fig. 2-b). From Figure 2-a and Figure 2-b, it isevident that the maximum variance of NDVI values is
at wavelength 755 and 679 nm, respectively, and thesame values are maintained when they are calculatedby different definite spectral reflectance values.
3.2 Difference in leaf necrosis between thewindward and leeward sides of ginkgo trees
It was observed that some landscape trees
showed necrosis from the leaf tip and margin to theentire leaf after Typhoon 0613 hit, in which a large

Fig. 3 Percentage of leaves with different necrotic levels
for the windward and leeward sides of ginkgo
trees sampled from Yamaguchi University.
During the investigation, all leaves on the
branches were visually counted into five levels,
which were 0, 1-30, 31-60, 61-99, and 100%.

Fig. 4 Relation between the necrotic area percentage(NAP) and NDVI755nm/679nm value.
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WANG FEI, H. YAMAMOTO, Y IBARAKI, K. IWAYA, N. TAKAYAMA

deciduous tree species can be seen from NDVIr. The
NDVIr of the crown is 43.9, 47.3, 43.6, and 75.1,
respectively, for the sampled trees of ginkgo, metasequoia, trident maple, and kaizuka juniper. The difference among ginkgo, metasequoia, and trident maple
was clearly smaller than the difference between thethree deciduous trees and the kaizuka juniper. The
reason seems to be the necrotic leaves on the windward side of these deciduous trees and the different
spectral reflectance sensitivity to them.

3.3 Spectral reflectance of necrotic leaves ofdifferent tree species
As mentioned above, many plants can show
symptoms of leaf necrosis by damage due to extreme
environmental conditions (Treshow, 1970). Spectralreflectance may be adopted to evaluate the necrotic
status of other tree species besides ginkgo. By spectral reflectance analysis of leaves sampled from thewindward and leeward sides of tree crowns after being hit by Typhoon 0613, the kaizuka juniper, an evergreen typhoon damage-resistant tree species (Shimizu,
2004), obviously differed from the other three deciduous tree species. Almost no difference between thewindward and leeward sides of the crowns of kaizuka
juniper was found in the spectral reflectance curves
since there was no necrosis of their leaves. For theother three deciduous tree species, the spectral reflectance curves between the windward and leeward sides
can be clearly distinguished because there are more
necrotic leaves on the windward side (refer to Fig. 5).
From Table 1, a very clear difference between
the evergreen kaizuka juniper and the other three

Table 1. NDVI and NDVI using ratios (NDVIr) value
for necrotic leaves of 4 tree species

GinkgoMetasequoia
Trident maple
Kaizuka juniper

NDVI (755 nm/679 nm)
Windward
Leeward
0.098
0.781
0.166
0.780
0.167
0.705
0.753
0.750

NDVIr*
43.9
47.3
43.6
75.1

* NDVIr is the NDVI value using ratios, which is the
proportion of NDVI755nm/679nm for the leaves of thewindward side to NDVI755nm/679nm for the leaves of theleeward side.

Fig. 5 Spectral reflectance curves for necrotic leaves sampled from the leeward side (○─○) and windward side (∆─∆)
of four tree species, in which ginkgo (Figure 5-a), metasequoia (Figure 5-b), and kaizuka juniper (Figure5-d) were sampled from shelterbelts, and trident maple (Figure 5-c) was sampled from an individual tree.
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ESTIMATION OF GINKGO LEAF NECROSIS INDUCED BY TYPHOON 0613 WITH SPECTRAL REFLECTANCE

3.4 Difference in leaf necrosis among different sites
According to this study, the spectral reflectanceof leaf samples from sites with different DC also varied significantly. Figure 6 shows that almost all leaves
sampled from ginkgo trees at Site A, which is morethan 40 km from the coastline, were mainly nonnecrotic leaves. By contrast, most leaf samples from
Site C, less than 2 km from the coastline, were necrotic leaves and dried leaves. The leaf samples from SiteB, about 13 km from the coastline, were in the middle
position. Therefore, the difference in storm-damaged
ginkgo leaves among sites was mainly due to thedifference in the percentage of leaves with varying
levels of necrosis after Typhoon 0613. The nearer tothe coastline, the more leaves there are with serious
necrosis after being hit by a typhoon.

Fig. 6 Percentage of leaves with different necrotic levels
for ginkgo trees sampled from three sites (Site A,
Site B, and Site C) by the visual scale method.
During the investigation, all leaves on the
branches were visually counted into five levels,
which were 0, 1-30, 31-60, 61-99, and 100%.
Fig. 7 Spectral reflectance curve for necrotic leaves
sampled from the leeward side (○─○) andthe windward side (▲─▲) in three sites withdifferent distances from the coastline (DC),in which 7-a, 7-b, and 7-c are respectively thedata for Site a, Site b, and Site c. Every line
was an average value of three duplications andthe NDVI value was calculated by the average
spectra reflectance values. Sampling andmeasurement were carried out on Nov. 1 andNov. 2, 2006 for Site A and Site B, and on Nov.
6 and Nov. 8, 2006 for Site C.

Figure 7 shows the spectral reflectance curvesof ginkgo leaves sampled from three sites after being
hit by Typhoon 0613. It is clear that there was also
a big difference in spectral reflectance among theleaves sampled from the windward and leeward sides
of ginkgo trees from the three sites. For the samples
from Site A, with an NDVI value of 0.679 for both theleeward and the windward side, respectively, the spectral reflectance curves almost overlapped each otherso that they could not be distinguished from eachother. This means almost no difference in leaf spectral
7

WANG FEI, H. YAMAMOTO, Y IBARAKI, K. IWAYA, N. TAKAYAMA

reflectance between the windward and leeward sides
of ginkgo trees at this site. Although the samples from
Site B and Site C showed a similar tendency whereby
the spectral reflectance curves between the windward
and leeward sides of the ginkgo trees were separate
from each other, we can clearly find a difference. The
spectral reflectance for the leaves of ginkgo trees at
Site B, with an NDVI value of 0.749 and 0.373 forthe leeward and the windward side, respectively, wassignificantly higher than that of Site C with an NDVI
value of 0.528 and 0.096 for the leeward and windward sides. This implies that Site C contained more
necrotic leaves. It is evident that the spectral reflectance characteristics are consistent with the result of
the visual scale observation.
Compared to the NDVI value, the NDVIr value
corresponded better to the damage status of ginkgo
trees, which combined the spectral reflectance of both
the windward and leeward sides. Figure 8 shows the
NDVIr, DC, maximum wind speed, and precipitation
during Typhoon 0613 for the three sites. The NDVIrvalues were respectively 67.9, 56.1, and 31.2 for Site
A, Site B, and Site C. The related maximum windspeeds were respectively 8, 20, and 27 m/s, rainfall,52, 26, and 14 mm, and distance from coastline, 40.1,
12.6, and 1.7 km. This means that the nearer to thecoastline, as the wind speed increased accompanying
the decrease in rainfall during Typhoon 0613 for theinvestigated sites, the smaller the NDVIr values were.
In other words, the nearer to the coastline, the greater
the leaf necrosis of ginkgo. The result of spectral reflectance was well in accordance with the differencein wind and precipitation. It was also consistent withthe result of the visual scale observations of other researchers (Okinaka et al., 1984).
4. Conclusion
Based on this research, it is the difference in leaf
necrotic status between the windward and leeward
sides of ginkgo crowns that causes the variance in discoloration between them. This kind of variation also
appears at sites of different distances from the coastline. They can be estimated by measuring the spectralreflectance of ginkgo leaves with different necrotic
status by using the pocket radiometer, EKO-MS720.

Fig. 8 NDVI using ratios (NDVIr, 8-a) value, distance from the coastline (DC, 8-b), maximum wind speed (8-c),
and precipitation (8-d) during the hit by Typhoon 0613 for the sampled leaves from three sites.
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ESTIMATION OF GINKGO LEAF NECROSIS INDUCED BY TYPHOON 0613 WITH SPECTRAL REFLECTANCE

The optimum wavelength for the calculation of NDVI
for necrotic ginkgo leaves is 679 and 755 nm. The
result of measurement of NDVI755nm/679nm is very consistent with the result of direct visual observation, andthe close inverse relationship between NDVI755nm/679nm
and NAP of ginkgo leaves indicates that it has potential to evaluate the damage status of ginkgo and to be
an alternative tool to measure leaf necrosis inducedby typhoons like Typhoon 0613, especially by using
the NDVIr value.
Comparison between ginkgo and three other tree
species indicated that spectral reflectance was moresensitive for the three deciduous tree species withnecrotic leaves than for the evergreen kaizuka juniper
tree without necrotic leaves. Ginkgo leaf necrosis is
a common sight in areas where typhoons frequently
occur, especially along the coast, where gingko leaves
show smaller NDVIr values.
Salisbury (1805) noted that great leaf injury occurred when rain was not associated with strong wind.
The rainless or low-rainfall period during and after
Typhoon 0613 reveals that the ginkgo leaf necrosis in
Yamaguchi City is just like Salisbury’s note.

growth, Vol. 5,” (Kozlowski T. T., ed.), Academic
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Hinzman, L. D., Bauer M. E., and Daughtry C. S. T., 1986:
Effects of nitrogen fertilization on growth and reflectance characteristics of winter wheat. Remote Sens.
Environ., 19,

47-61.

Holben, B. N., Schutt J. B., and McMurtrey J., 1983: Leaf
water stress detection utilizing thematic mapper bands
3, 4 and 5 in soybean plants. Int. J. Remote Sens., 4,289-297.
Ito, K., Otsuki, K., and Kamichika, M., 1996: Independent
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Water shortage and salinization diagnosis of grass byspectra reflectance. J. Agric. Meteorol., 59, 199-204 (inJapanese).
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Maki, T., Suzuki, Y., Kamoda, F., Hayakawa, S., andAcknowledgements

Tomari, K., 1991: Agricultural disaster from meteorol-This study was performed at the Research Laboratory of Environmental Ecology, Faulty of Agriculture, Yamaguchi University. We would like to express
our gratitude to all members who helped our measurement of spectral reflectance.

ogy and countermeasures, Yokendo, pp. 110-137 (inJapanese).
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