[DVI
1dy.
be
“cal
nog
the
lost
ship
in
zu ha
iual
N à
vith
7er,
ving
Fall
2 la-
LES
lese
his
Fied
ting
rent
ndex
by
calculating the ;NDVIo' have ob&en
shown, empirically and
theoretically, to be related) to
fAPAR in vegetation canopies
(Ruimy- et.al-,.19949 I Although
there are several possible
jimitations to such an
inference, it.'does "appear that
an epproximation of-chis fAPAR
can. be derived from the NDVI
(Myneni and Williams, 1994.
Ruimy et.altv. (309949, S938fter an
extensive Search ‘through °the
literature, tabulated various
relationships between fAPAR and
NDVI developed by different
workers. Forli Ehe, present, study
relationship based on SATL
model simulation was used which
is represented as:
FAPAR = -0.31+1.33*NDV]
The '10 day composited NDVI> data
was first averaged to give
average monthly NDVI for. laii
che Jcthree^yvears. Calibrations
for negative values on land in
the NDVI data were made din way
to set the bare: soil fAPAR to
zero. This calibrationmkrequired
a uniform. enhancement. of 9.1
NOVI units in. the: data. From
average monthly NDYVI;, fAPAR for
each month was calculated using
the above equation.
5.2 Absorbed Photosynthetically
Active Radiations (APAR)
The APAR ‘calculations: required
IPAR ‘and fAPAR data sets for
India. Monthly TAPAR ^data get
of India for: ithe [three years
Was generated’ as described in
the previous step. ‘The “monthly
Indian IPAR data extracted from
TOMS global data set of .Dye
(1995) was scombined with the
respective; fAPAR data to giye
monthly APAR in MJ m :
Assuming the agricultural areas
mapped above as constant for
ail the three years, the
agricultural APAR was extracted
using the agricultural areas
mask already generated.
5.3 Agricultural NPP, biomass
and production
Agricultural "NPP is defined dn
the "present study as the ^ dry
matter (both “above ground: and
below ground) produced pér unit
agricultural area and, biomass
as the total ary matter
Produced. Production is defined
es the dry matter partitioned
into economic yield.
The conversion. ofo^APAR - into
productivity requires COnVver-
sion elficiencies sof APAR: into
dry matter (es) of various
Crops. Since we ‚had only. an
agricultural areas map where
301
different crops are not identi-
fied, therefore, a mean, conver-
sion. efficiency value for iialll
the Cult ivat ions is required
forececuse Intithe ‘model. Ruimy
et.al (1994) conducted an
extensive literature survey and
tabulated tne € values for
different 'tCypes of ^vegetation
reported byil.dgdifferent workers.
puttmost of:*the workers report:
ed ve.tvalues.in terms ‘of. above
ground dry matter only. TO
Overcome this‘ problem they also
seanched through Chess literature
to lestimate.5a mean. ratio. of
below ground NPP to above
ground NPBS and arrived at Sa
value of 0.24 for.cultivatiorns.
Based on this factor they
arrived ar ‚a ‚Mean € value of
2.07 g dry matter (above ground
and below ground) MJ of APAR
for) cultivations For’ converting
APAR- datasiüntos NPP. This value
was usedio'for^' converting APAR
data into. agricultural NPP and
biomass in the present study.
The biomass can. be! converted to
agricultural production using
thet (Harvest Index © (HD): values
of! various: cropst.S HI valuest for
major: summer: and winter. crops,
locally>"known as Kharif and
Rabi crops, respectively, were
collected through literature
Survey. An area weighted aver-
age HI for summer and winter
season cCvops waso/calculated:s*as
05 2775. and 0.279, respectively.
These values were used to
calculate :ohesmoncHly !produc-
tion from monthly NPP.
5.4 Annual and Interannual
variations in biomass and
production
The monthly agricultural NPP
and biomass produced in the
Indian Sterritory 'agdicalcul ated
using the above steps are shown
in table Lo. The NPP and
consequently biomass starts
building.supsin-oJanuary .efter
the Sowing of winter Season
Crops in December.’ It reaches
its peak in the month of
February/ March due to peak
vegetative: growthi of fithes crops
and then drops suddenly in
April due Lo harvesting of
winter Crops. The biomass
generation ‘remains’ ‘low in itahe
summer months of Mayj.and.-June
and again starts building up in
July/August due to onset of
monsoon and growth'":of^ summer
Ccrops. 7 This:?sagain reaches dts
peak in September/October and
then falls suddenly in November
due to harvesting of summer
crops-.csSowing :of:winter^' season
crops starts in the end Of
November or December and there-
fore, the biomass remains low
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
