Rice Crop Discrimination Using Single Date
RISAT1 Hybrid (RH, RV) Polarimetric Data
Deepika Uppala, Ramana Venkata Kothapalli, Srikanth Poloju, Sesha Sai Venkata Rama Mullapudi, and Vinay Kumar Dadhwal
Abstract
Rice is the most important food grain crop in India and
contributes to more than 40 percent of the country’s food grain
production. Spaceborne remote sensing offers economically
viable and accurate production and area statistics. The utility of
optical remote sensing in mapping rice cropped area is limited
by persistent cloud cover during monsoon season. Temporal
availability of
SAR
data has facilitated an operational procedure
to monitor the rice crop. The current study discriminates rice
crop, using single date hybrid polarimetric data available
from
RISAT
-1
SAR
. This was subjected to Raney m-
δ
, m-
χ
decompositions, and supervised classification was performed.
The accuracy was estimated using the field points. The results
were compared with rice map generated using optical sensor
Resourcesat-2
LISS-IV
and statistical data. The spatial agreement
between the estimate from
RISAT
-1 and
LISS-IV
data was found to
be 85 percent. The class kappa value was 0.94 and 0.92 for
LISS-
IV
and
RISAT
-1, respectively.
Introduction
In India, rice is the most important cereal food crop and
grown in more than 14 major states during the rainy (
Kharif)
season and also in many states during
rabi
season. In India,
the
Kharif
season accounts for more than 80 percent of the
rice cultivation. But the utility of optical remote sensing in
enumeration of rice cropped area is limited due to cloud
cover during monsoon. Several studies have mapped rice area
using optical data using
MODIS
at 500 m and 250 m meters
spatial resolution (Gumma
et al
., 2011a 2011b, and 2014) and
temporal
AWiFS
data ( Ramana
et al
., 2014), but it is limited
by coarse resolution. Research on rice crop monitoring using
microwave remote sensing data produced an operational
procedure that uses temporal amplitude
SAR
data for rice crop
enumeration. The basic requirement to achieve this is that
the data should be acquired at the transplantation stage and a
minimum of three temporal datasets have to be acquired and
processed for generating a reliable estimate. Hence, an attempt
has been made in the current study, to discriminate and moni-
tor the rice crop through the use of single date hybrid polari-
metric (
RH
,
RV
)
FRS
1 data available onboard
RISAT
-1 satellite.
The Radar Imaging Satellite-1 (
RISAT
-1) is the first space-
borne Hybrid Polarimetric
SAR
, operating in C-band (5.35
GhZ
), launched on 26 April 2012 by the Department of Space,
Government of India.
RISAT
-1
SAR
is capable of all-weather
imaging capability in
HH
,
VV
,
HV
,
VH
and hybrid polarizations,
at incidence angles ranging from 12° to 55°. The swath ranges
from 12 km in fine mode to 220 km in course resolution mode
with a repeat cycle of 25 days. The system is capable of ac-
quiring data in both right and left looks. The details are given
in Table 1.
T
able
1. S
ensor
S
pecifications
of
risat
-1
Mode
Polarization
Spatial
Resolution
( Meters)
Swath
(Km)
Coarse Resolution Scan SAR
(CRS)
HH/HV or VH/VV
or RH/RV
36
223
Medium Resolution Scan SAR
(MRS)
HH/HV or VH/VV
or RH/RV
18
115
Fine Resolution Strip Map (FRS2) HH, HV, VH & VV 10/4.6 25
Fine Resolution Strip Map
(FRS1)
HH/HV or VH/VV
or RH/RV
3.3/2.3 25
The Synthetic Aperture Radar (
SAR
), contrary to optical
sensors has all-weather capability. Microwaves respond to the
large scale crop structure such as size, shape, orientation of
leaves and the dielectric properties of the crop canopy. Crop
structure and plant water content vary as a function of crop
type, growth stage, and crop condition. Many successful stud-
ies on rice mapping with multitemporal
SAR
data are conduct-
ed using only amplitude data (Le Toan
et al
., 1989; Haldar
et
al
., 2010; Kun Li
et al
., 2012; Qin Ma
et al
., 2013). From
these studies, rice and non-rice were classified based on the
temporal analysis of
SAR
backscatter. The freshly transplanted
rice plant gives very low backscatter value due to specular
reflection from standing water present in the field (Ribbes
et
al.,
1999). As the plant grows and develops tillers, the radar
backscatter increases up to the reproductive stage due to vol-
ume scattering from the vegetation and multiple reflections
between the plants and water surface (Ribbes
et al
., 1999;
Panigraphy
et al.
, 1999). These methods for rice mapping use
only the intensity component and do not include the relative
phase between the two received channels. Consequently, the
previous analysis options are restricted essentially to ratios or
differences within their respective images. With the availabil-
ity of fully polarimetric data from Radarsat-2 the crop type
information can be provided by a single-date image if the
SAR
sensor acquires information at multiple polarization using
airborne C-band polarimetric data (McNarin
et al
., 2000).This
method uses the relative phase information between the two
channels which has caught the attention of researchers. With
the availability of hybrid polarimetric data from
RISAT
1, an
attempt was made for rice crop discrimination and classifi-
cation. The hybrid polarimetric data has been used for crop
Deepika Uppala is with the National Remote Sensing
Center, ISRO - International Crops Research Institute for the
Semi-Arid Tropics (ICRISAT), Hyderabad, MIG-107,Road
No:1,K.P.H.B Colony, Hyderabad, India
(
).
Ramana Venkata Kothapalli, Srikanth Poloju, Sesha Sai
Venkata Rama Mullapudi, and Vinay Kumar Dadhwal are
with the National Remote Sensing Center, ISRO - NRSC,
Balanagar, Hyderabad, India.
Photogrammetric Engineering & Remote Sensing
Vol. 81, No. 7, July 2015, pp. 557–563.
0099-1112/15/557–563
© 2015 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.81.7.557
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
July 2015
557
