## 1 Introduction
In the investigation, LIF/Mie maps from both SLIPI and \"conventional\" detection approaches were compared. The conventional approach was found to be affected by errors introduced by multiple light scattering even in spray defined as optically dilute (optical depth or OD \(\sim\)1). In contrast, in SLIPI-LIF/Mie, the multiple scattering effects were addressed, and calibration of LIF/Mie ratio was possible in this case. The 2D maps of droplets SMD extracted with SLIPI were found in good agreements with the PDA measurements. However, it is worth highlighting that the intensity contribution from the multiply scattered light is very difficult to predict and the observed differences between conventional and SLIPI showed in [21] can change with the collection angle, optical turbidity, droplets size, distribution of the droplets in the spray, etc. Nevertheless, the results reported in [21], have been further demonstrated for absolute droplet SMD mapping in air blast atomizer [22], hollow-cone sprays [23], and direct injection sprays [7; 24]. In another study, SLIPI-scan was used for 2D and 3D mapping of the local \(\upmu\)e in an air-assisted spray system with a maximum optical depth OD \(\sim\)3 [25]. The method was first verified on a cuvette containing a homogenous solution of scattering particles of known \(\upmu\)e = 0.13 mm\({}^{-1}\). In a similar study, the SLIPI-scan method has been verified using milk solutions of controlled concentrations [26]. In this article, SLIPI-LIF/Mie [21] and SLIPI-scan [25; 26] are combined to simultaneously record the following:  
* The fluorescence signal from droplets located in the spray region;
* The Mie scattering signal from droplets located in the spray region;
* The light intensity transmitted through the spray; using a cuvette containing a fluorescing liquid. The simultaneous recording ensures that the generated images of LIF/Mie signals and transmission imaging are from identical spray operating conditions. This significantly reduces the time it would usually take as compared with two measurements performed sequentially. Furthermore, the same area is viewed on the camera providing the same spatial resolution. Finally, the PDA measurements are utilized for the calibration, and therefore, are not simultaneous with SLIPI-based measurements. Unlike the method to deduce 2D maps of droplets LVF from backlight-illumination based microscopic setup shown in [12], here, PDA calibration and numerical calculations are implemented for LVF calculations. The PDA calibration is preferred over microscopic setup due to its larger dynamic range (smallest droplet diameter measured is up to 3 \(\upmu\)m) as compared with the microscopic method (smallest diameter \(\geq\)10 \(\upmu\)m). Therefore, this study demonstrates the combination of three optical methods supported by numerical calculations to measure droplets SMD, droplets N, and LVF from the same spray section probed by the laser sheet. The method is extended for intersecting the spray in several 2D layers by means of laser sheet scanning (with a step size of Z = 500 \(\upmu\)m). Finally, it is shown that several 2D layers can be combined to generate a 3D map of each individual spray quantity.