At this point, the ISO 9241-11 standard [9] states that usability is the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.The interaction with devices needs to be satisfactory for the users. The ISO/IEC 9126-1 [7] presents and details a two-part model for software product quality:Internal and external quality (see Figure 1): Internal Quality is the totality of attributes of the software product from an internal view, e.g., spent resource. It is measured and improved during the code implementation, reviewing and testing. External Quality is the quality when software is running in terms of its behavior, e.g., number of wrong expected reactions.

It is measured and evaluated for software testing in a simulated environment [8].Figure 1.Quality model for external and internal quality [7].Quality in use (see Figure 2): It is the capability of the software product to enable specified users to achieve specified goals with effectiveness, productivity, safety and satisfaction in specified contexts of use.Figure 2.Quality model for quality in use [7].However, the design process becomes troublesome because of the nature of each user. Users are very different from each other. They like different things and they sense and perceive in different ways. Moreover, they have different capabilities. Besides, there are several groups which suffer these differences more deeply: people with disabilities and the elderly.

The first group suffers from different disabilities which are responsible for limiting several capabilities in a certain way. For example, users with sight disabilities will suffer from interaction problems with their devices if this interaction is based on visual stimulus, e.g., using a device display. On the other hand, elderly people usually suffer from similar interaction troubles due to their aging. As their senses tend to tire their capabilities and interaction levels decrease [5]. Current technology trends try to reduce the interaction barriers that elderly suffer with current devices. Mobile phones have audio control interaction and screen magnification, TVs have zoom and subtitles capabilities, etc. Nevertheless, the elderly are used to the products they already know [10,11].

For these groups the designed devices should be:Easy to use, so the users are able to use them to their own purposes.��Easy to learn��. This way, the final purpose of the device should be affordable in an acceptable time interval.Easy to recall, so the users are able to remember how to interact with the device.Nonetheless, Anacetrapib we are not exempt of suffering from similar situations. There are many conditions which cause people without disabilities to feel like they have one.

It is the second approach we invest URL List 1|]# in this study. The motivation for this decision were the findings that the reflectance of snow in the near infrared (NIR) somehow depends on the specific surface area, a measure which is used to characterize snow structure [10, 11].Models derived from radiative transfer theory describe light scattering often on the basis of the concept of equivalent sphere diameter [6, 12, 13]. This concept is a crude approximation of the real snow. More recent approaches aim at including more realistic structural information of real snow structure: The grain is approximated by dielectric films, plates, needles, prisms and hexagonal particles [14, 15, 16, 17, 18].

In the study of [17] a ray tracing approach was presented which calculates scattering properties of single particles having complex geometries.

Therefore, geometric optics and the far-field diffraction approximation were applied. Ray tracing algorithms based on Monte Carlo technique are also used to describe radiative transfer [19]. Such approaches have the advantage that many different physical properties can easily be calculated. But the difficulty in Monte Carlo based ray tracing approaches is to determine the probabilities of the physical processes (e.g. diffraction, reflection, absorption) as well as the representation of the structure of a porous medium.A typical problem in radiative transfer modeling is the validation of the calculated results with measured data.

To overcome this gap we present in this study radiative transfer calculations at the same structure for which the reflectance is measured.

To reach this goal we used micro-tomography to image the microstructure of snow samples [20, 21] and used this structural information to model the radiative transfer. We modeled the radiative transfer within the snow samples using the Dacomitinib beam-tracing model (BTM) presented in [22]. This radiative transfer model we present here calculates coherent multiple scattering. The BTM was originally designed to model the radiative transfer in soils. Snow is a stronger scatterer and much lower absorber than soil. Thus, in case of snow the number of light beams which have to be processed is a couple of orders larger than in case Cilengitide of soil.

To make the calculations feasible we implemented a snow extension module in the BTM.The representation of three-dimensional snow structure and the beam tracing in three-dimensional space is expensive with respect to computer memory and computation time. Thus, the BTM was implemented to run in two-dimensional space. Reducing dimensionality from three to two dimensions causes loss of structured information.