Cloud phase identification based on brightness temperatures provided by the bi-spectral IR Camera of JEM-EUSO Mission

Antonio J De Castro,Fernando López,Irene Rodríguez,Isabel Fernández-Gómez,Susana Briz,M Doro

doi:10.1051/epjconf/20158903002

Abstract

Cloud information is extremely important to correctly interpret the JEM-EUSO telescope data since UV radiation coming from the Extensive Air Shower can be partially absorbed or reflected by clouds. In order to observe the atmosphere and clouds in the field of view of the UV telescope the JEM-EUSO system will include an Atmospheric Monitoring System, which consists of a LIDAR and an IR Camera. Until now several radiative algorithms have been developed to retrieve the cloud top temperature from the brightness temperatures (BT) that the IR Camera will provide in two IR spectral bands (10.8 and 12 μm). In some cases the performance of the algorithms depends on cloud phase: water, ice or mixed. For this reason the identification of the cloud phase is valuable information for the correct interpretation of the cloud temperatures retrieved by radiative algorithms. Some previous proposals based on brightness temperature differences (BTD) have revealed that it is not easy to determine unambiguously the phase. In this work we present criteria to retrieve the cloud phase based on IR Camera BTDs. It has been checked with MODIS images to evaluate the possibilities to identify cloud phase with the JEM-EUSO IR Camera.

Highlights

The knowledge of cloud parameters such as the phase, the emissivity and other cloud propertiesare essential to understand issues as important as the radiative balance which rules drives the global climate change [1,2,3]
In order to observe the atmosphere and clouds in the field of view of the UV telescope the JEM-EUSO system will include an Atmospheric Monitoring System, which consists of a LIDAR and an IR Camera
Until now several radiative algorithms have been developed to retrieve the cloud top temperature from the brightness temperatures (BT) that the IR Camera will provide in two IR spectral bands (10.8 and 12 μm)

Summary

Introduction

The knowledge of cloud parameters such as the phase (water, ice or mixed), the emissivity and other cloud propertiesare essential to understand issues as important as the radiative balance which rules drives the global climate change [1,2,3]. In this work the objective of the cloud classification is to provide useful information for the analysis of the JEM-EUSO IR Camera data, especially for the cloud height retrieval. After calibration process, the IR camera will provide the brightness temperature (BT) in two 1-μm width spectral bands centred at 10.8 and 12 μm, hereinafter referred as BT11 and BT12 [10] From these BTs, Cloud Top Height (CTH) retrieval can be performed using radiometric information or stereovision technique [11, 12], this paper focuses on the first technique. The objective of the work here presented is to evaluate the capabilities of the IR camera to provide information about the type of cloud from the brightness temperature (BT) measured in its two spectral bands.

Clod top height retrieval

Classification of water and ice clouds from BTDs between BT11 and BT12

Identification of ice thin clouds from BTDs and BT11 thresholds

Conclusions