*Article* **Mitigation of Systematic Noise in F16 SSMIS LAS Channels Observations for Tropical Cyclone Applications**

**Huijie Dong and Xiaolei Zou \***

Joint Center of Data Assimilation for Research and Application, Nanjing University of Information Science & Technology, Nanjing 210044, China; hdong@nuist.edu.cn

**\*** Correspondence: xzou@nuist.edu.cn

**Abstract:** The Special Sensor Microwave Imager Sounder (SSMIS) onboard the Defense Meteorological Satellite Program (DMSP) F16, launched on 18 October 2003, was the first conical-scanning radiometer to combine the Special Sensor Microwave/Imagers (SSM/I), Special Sensor Microwave/ Temperature Sounder (SSM/T), and the Special Sensor Microwave/Water Vapor Sounder (SSM/T2). Nearly 20 years of F16 SSMIS data are available to the general public, providing many opportunities to study the atmosphere at both the synoptic and decadal scales. However, data noise from complicated structures has occurred in the brightness temperature (TB) observations of lower atmospheric sounding (LAS) channels since 25 April 2013. We used a two-dimensional Fast Fourier Transform to analyze the characteristic features of data noise in cross-track and along-track directions. We found that the data noise is around 1–2 K and occurs at certain cross-track wavelengths (Δ*λ*)*noise*. A latitudinal variation was found for (Δ*λ*)*noise*. Due to noise interference, TB observations reflecting rain, clouds, tropical cyclone warm core, temperature, and water vapor distributions are not readily distinguishable, especially in channels above the middle troposphere (channels 4–7 and 24), whose dynamic TB range is smaller than low tropospheric channels 1–3. Examples are provided to show the impact of the proposed noise mitigation for conical-scanning TB observations to capture 3D structures of hurricanes directly. Once the noise in F16 SSMIS LAS channels from 25 April 2013to the present is eliminated, we may investigate the decadal change of many features of tropical cyclones derivable from these TB observations.

**Keywords:** F16 SSMIS LAS channels; brightness temperature observations; along-track varying cross-track data noise; tropical cyclone
