Aqua/AIRS L2 Near Real Time (NRT) Standard Physical Retrieval (AIRS-only) V7.0 at GES DISC

The Atmospheric Infrared Sounder (AIRS) Level 2 Near Real Time (NRT) Standard Physical Retrieval (AIRS-only) product (AIRS2RET_NRT_7.0) differs from the routine product (AIRS2RET_7.0) in four ways to meet the three hour latency requirements of the Land Atmosphere NRT Capability Earth Observing System (LANCE): (1) The NRT granules are produced without previous or subsequent granules if those granules are not available within 5 minutes, (2) the predictive ephemeris/attitude data are used rather than the definitive ephemeris/attitude, (3) if the forecast surface pressure is unavailable, a surface climatology is used, and (4) no ice cloud properties retrievals are performed. The consequences of these differences are described in the AIRS Near Real Time (NRT) data products document. The Atmospheric Infrared Sounder (AIRS) is a grating spectrometer (R = 1200) aboard the second Earth Observing System (EOS) polar-orbiting platform, EOS Aqua. In combination with the Advanced Microwave Sounding Unit (AMSU) and the Humidity Sounder for Brazil (HSB), AIRS constitutes an innovative atmospheric sounding group of visible, infrared, and microwave sensors. This product is produced using AIRS IR only because the radiometric noise in several AMSU channels started to increase significantly (since June 2007). The AIRS Standard Retrieval Product consists of retrieved estimates of cloud and surface properties, plus profiles of retrieved temperature, water vapor, ozone, carbon monoxide and methane. Estimates of the errors associated with these quantities is also part of the Standard Product. The temperature profile vertical resolution is 28 levels total between 1100 mb and 0.1 mb, while moisture profile is reported at 14 atmospheric layers between 1100 mb and 50 mb. The horizontal resolution is 50 km.

An AIRS granule has been set as 6 minutes of data, 30 footprints cross track by 45 lines along track. There are 240 granules per day, with an orbit repeat cycle of approximately 16 day.

大气红外探空仪（Atmospheric Infrared Sounder, AIRS）二级近实时（Near Real Time, NRT）仅基于AIRS的标准物理反演产品（AIRS2RET_NRT_7.0）与常规产品（AIRS2RET_7.0）存在四项差异，以满足陆地大气近实时能力地球观测系统（Land Atmosphere NRT Capability Earth Observing System, LANCE）的3小时延迟要求：
1. 若5分钟内无法获取前序或后续数据粒，则仅单独生成该近实时数据粒；
2. 采用预测星历/姿态数据，而非精密星历/姿态数据；
3. 若预报地表气压不可用，则采用地表气候学数据替代；
4. 不执行冰云属性反演。
上述差异带来的影响已在《AIRS近实时（NRT）数据产品文档》中详述。

大气红外探空仪（AIRS）是搭载于第二代地球观测系统（Earth Observing System, EOS）极轨平台EOS Aqua上的光栅光谱仪（分辨率R=1200）。其与先进微波探空仪（Advanced Microwave Sounding Unit, AMSU）以及巴西湿度探空仪（Humidity Sounder for Brazil, HSB）协同工作，共同构成一套创新性的可见、红外及微波大气探空传感器组。本产品仅采用AIRS红外数据生成，原因是自2007年6月起，AMSU多个通道的辐射噪声出现显著升高。

AIRS标准反演产品涵盖云与地表属性的反演估算值，以及温度、水汽、臭氧、一氧化碳和甲烷的垂直廓线反演结果；各参量对应的误差估算值同样为标准产品的组成部分。其中温度廓线在1100毫巴至0.1毫巴范围内具备28层垂直分辨率，水汽廓线在1100毫巴至50毫巴范围内提供14层大气廓线数据。该产品的水平分辨率为50千米。

单AIRS数据粒对应6分钟的观测数据，包含30个跨轨像幅与45个沿轨扫描线。每日可生成240个数据粒，轨道重复周期约为16天。