A satellite radiance-bias correction scheme for data assimilation
A satellite radiance-bias correction scheme for data assimilation
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DOI：
10.1002/qj.49712757418
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发表时间：
2001-04-01
影响因子：
8.9
通讯作者：
Kelly, G
中科院分区：
文献类型：
--
作者：
Harris, BA;Kelly, G
最近，在数值天气预报系统中直接同化卫星辐射测量方面取得了很大进展。为了使用 TIROS 操作垂直探测器 (TOVS) 的辐射率，必须纠正观测到的辐射率与模型首次猜测模拟的辐射率之间的偏差。欧洲中期天气预报中心的 TOVS 辐射偏差校正的原始方案利用了全局扫描校正和线性气团校正，并以微波探测装置通道 2、3 和 4 观测到的辐射作为预测因子。新方案在两个基本方面有所不同。辐射数据分析显示存在显着的残余扫描偏差，该偏差很大程度上取决于某些通道的纬度。新方案应用纬度相关扫描校正来考虑这一点。现在，空气质量预测因子是根据背景场计算的，因为背景场包含比观测到的微波辐射更一致的空气质量和表面特征表示。使用四个新的预测因子：1000-300 hPa 厚度、200-50 hPa 厚度、模型表面表皮温度和总可降水量。特别是，皮肤温度预测器能够区分海洋和海冰，在冬半球的表现比旧方案好得多。模型预测器的使用是哲学上的转变，从校正观测到校正计算的前向辐射率。这导致了一种自然的扩展，其中可以在变分检索方案中考虑偏差校正的梯度。
Recently, much progress has been made in the direct assimilation of satellite radiance measurements in numerical weather-prediction systems. In order to use radiances from the TIROS Operational Vertical Sounder (TOVS), biases between the observed radiances and those simulated from the model first guess must be corrected. The original scheme for TOVS radiance-bias correction at the European Centre for Medium-Range Weather Forecasts utilized a global scan correction, and a linear air-mass correction, with the observed radiances from the Microwave Sounding Unit channels 2, 3 and 4 as predictors. The new scheme differs in two fundamental ways. Analysis of radiance data shows a significant residual scan bias which depends strongly on latitude for some channels. The new scheme applies a latitudinally dependent scan correction to take this into account. The air-mass predictors are now computed from the background field, since the background field contains a more consistent representation of the air mass and surface characteristics than the observed microwave radiances. Four new predictors are used, 1000-300 hPa thickness, 200-50 hPa thickness, model surface skin temperature and total precipitable water. In particular, the skin-temperature predictor is able to differentiate between ocean and sea-ice, performing much better than the old scheme in the winter hemisphere. The use of model predictors is a change in philosophy away from correction of the observations to correction of the computed forward radiances. This leads to a natural extension where the gradient of the bias correction can be taken into account in variational retrieval schemes.