We present an updated version of the multilayer spectral inversion (MLSI) recently proposed as a technique to infer the physical parameters of plasmas in the solar chromosphere from a strong absorption line. In the original MLSI, the absorption prole was constant over each layer of the chromosphere, whereas the source function was allowed to vary with optical depth. In our updated MLSI, the absorption prole is allowed to vary with optical depth in each layer and kept continuous at the interface of two adjacent layers. We also propose a new set of physical requirements for the parameters useful in the constrained model tting. We apply this updated MLSI to two sets of Hα and Ca ii line spectral data taken by the Fast Imaging Solar Spectrograph (FISS) from a quiet region and an active region, respectively. We nd that the new version of the MLSI satisfactorily ts most of the observed line proles of various features, including a network feature, an internetwork feature, a mottle feature in a quiet region, and a plage feature, a superpenumbral bril, an umbral feature, and a fast down ow feature in an active region. The MLSI can also yield physically reasonable estimates of hydrogen temperature and nonthermal speed as well as Doppler velocities at different atmospheric levels. We conclude that the MLSI is a very useful tool to analyze the Hα line and the Ca ii 8542 line spectral daya, and will promote the investigation of physical processes occurring in the solar photosphere and chromosphere.

Abstract
1. INTRODUCTION
2. DATA AND REDUCTION
3. UPDATED MLSI MODEL
    3.1. Photospheric Layer
    3.2. Chromospheric Layers
    3.3. Model Fitting
    3.4. Initialization
    3.5. Computing Time
4. RESULTS
    4.1. Temperature of Chromospheric Features
    4.2. Maps and Statistics of Model Parameters
    4.3. Individual Features
5. SUMMARY AND DISCUSSION
REFERENCES

• Jongchul Chae(Astronomy Program, Department of Physics and Astronomy, Seoul National University) Corresponding author
• Kyuhyoun Cho(Astronomy Program, Department of Physics and Astronomy, Seoul National University)
• Juhyung Kang(Astronomy Program, Department of Physics and Astronomy, Seoul National University/Solar and Space Weather Group, Korea Astronomy and Space Science Institute)
• Kyoung-Sun Lee(Astronomy Program, Department of Physics and Astronomy, Seoul National University)
• Hannah Kwak(Astronomy Program, Department of Physics and Astronomy, Seoul National University)
• Eun-Kyung Lim(Solar and Space Weather Group, Korea Astronomy and Space Science Institute)