B.rightness Temperature

Overview

The brightness temperature is a measurement of the radiance of the microwave radiation traveling upward from the top of the atmosphere to the satellite, expressed in units of the temperature of an equivalent black body. The brightness temperature (or TB.)是由被动的基本参数测量microwave radiometers. The brightness temperatures, measured at different microwave frequencies, are used at Remote Sensing Systems to derive wind, vapor, cloud, rain, and SST products. Despite differences in sensor frequencies, channel resolutions, instrument operation and other radiometer characteristics, RSS produces high-quality, carefully intercalibrated data,using uniform processing techniques, with a brightness temperature data record spanning multiple instruments over several decades. At the bottom of this page, we include information on access to our brightness temperature data and links to more detailed information.

What is Brightness Temperature?

Satellite passive microwave radiometers measure raw antenna counts from which we determine the antenna temperature and then calculate the brightness temperature of the Earth. Large antennas are used for the various channels of the radiometer, and during operation, each antenna feedhorn passes a hot and cold target in order to provide consistently calibrated raw counts. Brightness temperature (also referred to as TB) is a measure of the radiance of microwave radiation traveling upward from the top of Earth's atmosphere. The conversion from radiometer counts to top-of-the-atmosphere TB is called the calibration process. Several calibration processing steps are required to derive the TB values. Microwave radiometer TB are considered a fundamental climate data record and are the values from which we derive ocean measurements of wind speed, water vapor, cloud liquid water, rain rate, and sea surface temperature.

我们从NASA,NOAA,DMSP或NRL等数据源获得每个微波辐射计的天线温度数据文件。为确保气候质量,校准的海洋产品数据集,我们首先将这些文件中的数据逆转到原始辐射计天线计数。该过程删除了数据提供者可能添加的校正或调整。一旦我们有原始计数,我们就前进如下所述。

处理方法

从原始辐射计数计算TB是一个复杂的多步骤,其中必须准确地表征多种效果,并对它们进行审计。这些效果包括辐射计非线性,校准目标中的缺陷,主要天线的发射和天线图案调整。RSS TB一致地校准,使得所有传感器的TB测量可用于构造多码时间序列。乐动体育官方2.0乐动苹果手机无雨的海洋用作绝对校准参考,以及我们在没有雨中的缺失的海洋和干预气氛中的绝对校准参考和我们最先进的气氛可以预测大气层TB高精度。一套完整的description of the calibration of all SSM/Iis available. Though the document describes on SSM/I sensors, the approach applies to the other radiometers.

Several of the steps necessary are summarized in the table below by microwave radiometer and are discussed further below.

Calibration Steps for Microwave Radiometers

Geolocation Analysis

Attitude Adjustment

沿扫描校正

绝对校准

Hot Load Correction

天线发射率

SSM / I. NRL/RSS No Yes APC No 0.
SSMIS rss. No Yes APC Yes 0..5-3.5%
TMI rss. Dynamic Yes APC No 3.5%
温莎特 NRL/RSS Fixed Yes APC Yes 0.
AMSRE rss. Fixed Yes APC Yes 0.
AMSR2 rss. No Yes APC Yes 0.

第一步是地理位置。知道任何后续搭配或进行的每次测量所需的确切位置。我们使用升序减去降价,看看小海岛,并确保它们不会“移动”。Geolocation并不总是由RSS执行,如表[NRL =海军研究实验室,GSFC = Goddard Space Vistram Center]所示。乐动帐号注册对地理定位的校正与仪器安装误差的校正不同(也称为辊/俯仰/横摆校正)也必须寻址。

The remaining corrections listed in the table are performed by comparing antenna temperatures with those simulated by our radiative transfer model. The Remote Sensing Systems' atmospheric radiative transfer model (RTM) for the ocean surface and intervening atmosphere has been continually developed and refined for more than 30 years, and is highly accurate in the 1-100 GHz (microwave) spectrum for ocean observations. The ocean surface model components include polarimetric wind speed and direction with dependencies on surface emissivity and scattering. The atmospheric components of our RTM rely on the most recent and relevant measurements of oxygen and vapor.

Attitude adjustment includes correcting for spacecraft pointing errors. Spacecraft pointing is determined by a number of different methods, the preferred being a star tracker. Another method is horizon balancing sensor. For SSM/I no pointing information was given, so it was assumed to be correct. TMI has a dynamic pointing correction that changes within an orbit because the horizon sensor used prior to the orbit boost is not as accurate as a star tracker. After orbit boost, the horizon sensor was disabled and pointing was determined from two on-board gyroscopes, also not as accurate as a star tracker. AMSR-E had no pointing problems, as the AQUA satellite had a star tracker. The AMSR on ADEOS-II needed a dynamic correction, while WindSat needed a simple fixed correction to the roll/pitch/yaw.

镜子旋转,地球sc的边缘ene view will begin to contain obstructions such as the satellite itself or part of the cold mirror. Additionally, during the scan, the antenna sidelobe pattern may result in contributions from different parts of the spacecraft. Every instrument needs this along-scan correction.

接下来我们执行天线模式校正(APC)。APC是确定预启动的,并且由溢出和交叉极化值组成。在发射之后,调整溢出和交叉偏振值,使得测量的天线温度与RTM模拟的天线温度匹配。所有乐器都需要这种校正。

只有一些辐射仪需要热负荷热梯度校正。使用两种已知的温度完成从微波辐射仪计数的TB的测定来推断地球场景温度。对于每次扫描,天线进料堆观察反射冷空间的镜子(已知温度为2.7 k)和由几个热敏电阻测量的热吸收器。假设线性响应,然后通过将斜率拟合到这两个已知的测量(热和冷)来确定地球场景温度。乐动体育官方2.0乐动苹果手机该2点校准系统连续补偿辐射计增益和噪声温度的变化。这种看似简单的校准方法充满了微妙的困难。冷镜相对无故障,只要我们在寒冷的空间视图上侵入时,我们会注意到寒冷的空间视图并移除受月亮影响的值。热吸收器更为有问题。热敏电阻通常不会在热吸收器上充分测量热梯度。例如,AMSR-E需要热负荷校正,因为AMSR-E热负荷中的设计缺陷。 The hot load acts as a blackbody emitter and its temperature is measured by precision thermistors. Unfortunately, during the course of an orbit, large thermal gradients develop within the hot load due to solar heating making it difficult to determine the average effective temperature from the thermistor readings. The thermistors themselves measure these gradients and may vary by up to 15 K. Several other radiometers have had similar, but smaller, issues.

Lastly, the main reflector is assumed to be a perfect reflector with an emissivity of 0.0, but this is not always the case. A bias in the TMI measurements was attributed to the degradation of the primary antenna as atomic oxygen present at TMI’s low altitude (350 km) led to rapid oxidization of the thin, vapor-deposited aluminum coating on the graphite primary antenna. The measured radiation is therefore comprised of the reflected Earth scene and antenna emissions. Emissivity of the antenna was deduced during the calibration procedure to be 3.5%. The antenna emissivity correction utilizes additional information from instrument thermistors to estimate the antenna temperature, thereby reducing the effect of the temporal variance. This emissivity is constant for all the TMI channels. The SSMIS instruments also has an emissive antenna where the emissivity appears to increase as a function of frequency, changing from 0.5 to 3.5 %.

Data Availability and Access

B.rightness temperatures are treated as an intermediate product, not a typical Earth Systems Data Record (ESDR). Our brightness temperature data for various instruments are available via different data centers listed in the table below.

Instrument/Satellite rss.B.rightness Temperature Data Availability
Table of Brightness Temperature Access by Instrument (updated Aug 2014)

SSMI on DMSP
(F08,F10,F11,F13,F14,F15)

RSS V7 TBS在NETAA NCDC以NETCDF格式分发

SSMIS on DMSP
(F16, F17)

RSS V7 TBS在NETAA NCDC以NETCDF格式分发
温莎特on Coriolis rss.V7 TBs not publicly available
TMI在TRMM上 rss.V7 TBs not publicly available
AMSR-E on Aqua rss.V7 TBs distributed by NSIDC(note: NSIDC uses a different version number in their system)
AMSR2 on GCOM - W1 rss.V7 TBs not publicly available

There are two documents available that further describe the contents of the netCDF RSS V7 TB data products for SSM/I and SSMIS (see links at left).

在以下时间段期间,SSM / I和SSMIS传感器可用于SSM / I和SSMIS传感器的亮度温度数据:

Instrument Start Date 停止日期
F08 SSM / I Jul 1987 Dec 1991
F10 SSM/I Dec 1990 Nov 1997
F11 SSM/I Dec 1991 May 2000
F13 SSM/I May 1995 Nov 2009
F14 SSM / I 1997年5月 2008年8月
F15 SSM / I Dec 1999 present (do not use after Aug 2006 for climate study)
F16 SSMIS Oct 2003 present
F17 SSMIS. 2006年12月 present
F18 SSMIS Oct 2009 目前(数据目前没有在RSS上获得)
F19 SSMIS. Apr 2014 目前(数据目前没有在RSS上获得)