Abstract
Abstract. Kim and van Zyl (2001) proposed a kind of radar vegetation index (RVI). RVI = 4*min(λ1, λ2, λ3) / (λ1 + λ2 + λ3) They modified the equation as follows. (2009) RVI = 8 * σ0hv / (σ0hh + σ0vv +σ0hv ) by L-band full-polarimetric SAR data. They applied it into rice crop and soybean. (Y.Kim, T.Jackson et al., 2012) They compared RVI for L-, C- and X-bands to crop growth data, LAI and NDVI. They found L-band RVI was well correlated with Vegetation Water Content, LAI and NDVI. But the field data were collected by the multifrequency polarimetric scatterometer. The platform height was 4.16 meters from the ground. The author tried to apply the method to actual paddy fields near Tsukuba science city in Japan using ALOS/PALSAR, full-polarimetry L-band SAR data. The staple crop in Eastern Asia is rice and paddy fields are dominant land use. A rice-planting machine comes into wide use in this areas. The young rice plants were bedded regularly ridged line in the paddy fields by the machine. The space between two ridges of rice plants is about 30 cm and the wave length of PALSAR sensor is about 23 cm. Hence the Bragg scattering will appear depending upon the direction of the ridges of paddy fields. Once the Bragg scattering occurs, the backscattering values from the pixels should be very high comparing the surrounding region. Therefore the radar vegetation index (RVI) would be saturated. The RVI did not follow the increasing of vegetation anymore. Japan has launched ALOS-2 satellite and it has PALSAR-2, L-band SAR. Therefore RVI application product by PALSAR-2 will be watched with deep interest.
Highlights
1.1 General Trend of Earth Observation SatellitesEarth observation satellites, which are launched recently, incline toward SAR satellite or the consternation of operation of small satellites which are usually loaded with visible and near infrared band optical sensors
ALOS/PALSAR JAXA processing level 1.1 data are converted into backscattering values as following equation.(Isoguchi, Shimada, 2007)
They applied it into rice crop and soybean. (Y.Kim, T.Jackson et al, 2012) Their experiment was performed by the L-band full polarization sensor above the field collecting data every 10 minutes during the crop grown season. They compared radar vegetation index (RVI) for L, C- and X-bands to crop growth data, LAI and NDVI. They found L-band RVI was well correlated with Vegetation Water Content, LAI and NDVI
Summary
Earth observation satellites, which are launched recently, incline toward SAR satellite or the consternation of operation of small satellites which are usually loaded with visible and near infrared band optical sensors. JAXA/ALOS-2 and NASA/SMAP satellite, which are most recently launched, are equipped with the L-band SAR sensor. From the viewpoint of agriculture, crop growth monitoring is desired but sometimes cloud cover interrupts ground surface observation. An index for crop growth monitoring using L-band SAR data is important. The platform height was 4.16 meters from the ground. They reported that the RVI is effective to estimate VWC, vegetation water content. Their VWC is useful for the estimation of soil moisture or drought, according to Kim and Jackson, et al..
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