###### Abstract
As the most widely used type of wireless communication, radio frequency (RF) communications suffer from severe electromagnetic interference (EMI): equipment used during normal mining operations such as drill machines, mine trucks, electric motors, and continuous miners operate in the same frequency range as radio communication devices, causing a significant amount of noise [4]. To complement the classical wireless communication systems deployed in UM, researchers have proposed the use of visible light communications (VLC), in which a light-emitting diode (LED) is intensity-modulated by a driving current at the transmitter (TX), producing a visible light signal that is detected by a photodiode (PD) that produces a photocurrent at the receiver (RX). The optical signal is modulated rapidly enough to be not perceived by the human eye, making VLC systems suitable for data transmission and illumination at the same time. Its immunity to EMI, relatively low cost, unlicensed frequency spectrum, support of high data rates, and the fact that underground mines already depend on artificial light sources for their functioning make VLC an attractive candidate for short-range wireless communications in underground mines [5; 6]. Although the VLC channel for classical indoor environments (i.e., regular buildings) has been studied well, the underground mining VLC channel (UM-VLC) has only recently been a topic of research interest. Over the past few years, several authors have proposed UM-VLC channel models that account for channel characteristics inherent to the UM environment that are not present in classical indoor environments. These include, but are not limited, to the relative tilt and rotation between LED and PD, irregular (i.e., non-flat) walls, light scattering and absorption due to dust, and shadowing (e.g., large machinery blocking the light signal) [7; 8]. However, to the best of the authors' knowledge, no UM-VLC channel model has been proposed in the literature that accounts for the wavelength's dependence of the aforementioned phenomena or the inherent spectral properties of LEDs and PDs. Although VLC channel models that do not account for wavelength dependency are suitable for VLC systems with monochromatic or narrowband light sources, illumination systems require white-light LEDs that are inherently wideband. [PERSON] and [PERSON] [9] argue that the wideband property of white light LEDs calls for the inclusion of wavelength dependency in VLC channel modeling and proceed to mention multiple research papers that propose wavelength-dependent classical in-door VLC channels. Furthermore, wavelength dependency becomes an even more important factor when considering color-domain-based VLC systems, in which the wavelength dependence of the channel is crucial to the system's performance. The most notable color-domain-based modulation scheme is known as color shift keying (CSK) modulation, in which data are encoded into the instantaneous optical power of RGB LEDs in such a way that the perceived color and the average transmitted optical are static [10]. This modulation scheme is included in the IEEE 802.15.7 standard [11] for high-data-rate applications with multiple light sources, where 4-CSK, 8-CSK, and 16-CSK constellations are defined. Most of the existing literature on the performance and channel modeling of CSK-based VLC systems considers classical indoor VLC channels with only a line-of-sight (LOS) component. Notable exceptions include the outdoor optical camera communications channel (OOC) [12], the underwater optical communication channel (UWOOC) [13], and the underwater wireless optical communication channel (UWOC) [14]. To the best knowledge of the authors, CSK-based UM-VLC systems have not been modeled or evaluated in the literature so far. In this work, we propose a wavelength-dependent UM-VLC single-input, single-output (SISO) channel model in which the spectral characteristics of the LED, the PD, the dust particles, and the reflective surfaces are considered.