Google Earth Engine ——全球 25m PALSAR/PALSAR-2資料集

The global 25m PALSAR/PALSAR-2 mosaic is a seamless global SAR image created by mosaicking strips of SAR imagery from PALSAR/PALSAR-2. For each year and location, the strip data were selected through visual inspection of the browse mosaics available over the period, with those showing minimum response to surface moisture preferentially used. In cases where the availability was limited (e.g., because of the requirement for observations during specific emergencies), data were necessarily selected from the year before or after, including from 2006. Shimada et al. 2014

The SAR imagery was ortho-rectificatied and slope corrected using the 90m SRTM Digital Elevation Model. A destriping process (Shimada & Isoguchi, 2002, 2010) was applied to equalize the intensity differences between neighboring strips, occurring largely due to seasonal and daily differences in surface moisture conditions.

Polarization data are stored as 16-bit digital numbers (DN). The DN values can be converted to gamma naught values in decibel unit (dB) using the following equation:

• γ₀ = 10log₁₀(DN²) - 83.0 dB

Attention:

• Backscatter values may vary significantly from path to path over high latitude forest areas. This is due to the change of backscattering intensity caused by freezing trees in winter.

全球 25m PALSAR/PALSAR-2 拼接圖是由 PALSAR/PALSAR-2 的 SAR 影像條帶拼接而成的無縫全球 SAR 影像。對于每一年和地點，條帶資料是通過目視檢查這段時間内可用的浏覽馬賽克來選擇的，優先使用那些對表面水分反應最小的那些。在可用性有限的情況下（例如，由于需要在特定緊急情況下進行觀察），必須從前一年或後一年中選擇資料，包括 2006 年。 Shimada 等。 2014年

使用 90m SRTM 數字高程模型對 SAR 圖像進行正射校正和斜率校正。去除條紋過程 (Shimada & Isoguchi, 2002, 2010) 用于平衡相鄰條紋之間的強度差異，這主要是由于表面水分條件的季節性和日常差異造成的。

偏振資料存儲為 16 位數字 (DN)。可以使用以下等式将 DN 值轉換為以分貝為機關 (dB) 的伽馬零值：

γ₀ = 10log₁₀(DN²) - 83.0 dB
注意力：

在高緯度森林地區，不同路徑的反向散射值可能會有很大差異。這是由于冬季樹木結冰引起後向散射強度的變化。      

Dataset Availability

2007-01-01T00:00:00 - 2021-01-01T00:00:00

Dataset Provider

JAXA EORC

Collection Snippet

Copied

ee.ImageCollection("JAXA/ALOS/PALSAR/YEARLY/SAR")

Resolution

25 meters

Bands Table

Name	Description
HH	HH polarization backscattering coefficient, 16-bit DN.
HV	HV polarization backscattering coefficient, 16-bit DN.
angle	Local incidence angle (degrees).
date	Observation date (days since Jan 1, 1970).
qa	Processing information.

Class Table: qa

Value	Color	Color Value	Description
#000000	No data
50	#0000FF	Ocean and water
100	#AAAA00	Radar layover
150	#005555	Radar shadowing
255	#AA9988	Land

 資料說明：JAXA retains ownership of the dataset and cannot guarantee any problem caused by or possibly caused by using the datasets. Anyone wishing to publish any results using the datasets should clearly acknowledge the ownership of the data in the publication. 

引用：

Masanobu Shimada, Takuya Itoh, Takeshi Motooka, Manabu Watanabe, Shiraishi Tomohiro, Rajesh Thapa, and Richard Lucas, "New Global Forest/Non-forest Maps from ALOS PALSAR Data (2007-2010)", Remote Sensing of Environment, 155, pp. 13-31, December 2014. doi:10.1016/j.rse.2014.04.014.

代碼：

var dataset = ee.ImageCollection('JAXA/ALOS/PALSAR/YEARLY/SAR')
                  .filter(ee.Filter.date('2017-01-01', '2018-01-01'));
var sarHh = dataset.select('HH');
var sarHhVis = {
  min: 0.0,
  max: 10000.0,
};
Map.setCenter(136.85, 37.37, 4);
Map.addLayer(sarHh, sarHhVis, 'SAR HH');