Google Earth Engine ——全球 25m PALSAR/PALSAR-2数据集

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 拼接图是由 PALSAR/PALSAR-2 的 SAR 影像条带拼接而成的无缝全球 SAR 影像。对于每一年和地点，条带数据是通过目视检查这段时间内可用的浏览马赛克来选择的，优先使用那些对表面水分反应最小的那些。在可用性有限的情况下（例如，由于需要在特定紧急情况下进行观察），必须从前一年或后一年中选择数据，包括 2006 年。 Shimada 等。 2014年

使用 90m SRTM 数字高程模型对 SAR 图像进行正射校正和斜率校正。去除条纹过程 (Shimada & Isoguchi, 2002, 2010) 用于平衡相邻条纹之间的强度差异，这主要是由于表面水分条件的季节性和日常差异造成的。

偏振数据存储为 16 位数字 (DN)。可以使用以下等式将 DN 值转换为以分贝为单位 (dB) 的伽马零值：

γ₀ = 10log₁₀(DN²) - 83.0 dB

注意力：

在高纬度森林地区，不同路径的反向散射值可能会有很大差异。这是由于冬季树木结冰引起后向散射强度的变化。

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

Class Table: qa

数据说明：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.

代码：

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');