mo 1000

Stiff OP particle, m'pcron

Figure 2: Sum of detected intensities for spheres (— ice,---silicate, •••• organics, carbon) and from microwave analog measurements for the aggregated particles (see Fig. 3).

Planetary aerosol monitor / interplanetary dust analyzer

From Mie calculations one can see that the sum intensity for the given scattering angles has almost no dependency on the composition of spherical particles. Results of the microwave measurements show that even for so complicated particles as the aggregates shown on Figure 3 the size of aggregate, determined independently by direct measurements of aggregate dimensions, can be well determined by measurements of the sum intensity of li scattered by the aggregates. The range of measured intensities corresponds to the meas ments for different orientations of aggregates. The vertical lines correspond to the avt e size of aggregates.

Figure 3: Aggregate 1: 500 spheres of size parameter (circumference to wavelength ratio) x= 1.5 each. Scaled to A=0.8 pm, the size of each sphere is 0.38 p,m and the dimension of the aggregate is 20 pm. Aggregate 2: 37 spheres of size parameter 20 each. Scaled to X=0.8 Jim, the size of each sphere is 5 (im and the dimension of the aggregate is 100 p.m. Aggregate 3: 43 spheres of size parameter jc= 20 each. Scaled to A=0.8 p,m, the size of each sphere is 5 pm and the dimension of the aggregate is 200 p.m.

Figure 3: Aggregate 1: 500 spheres of size parameter (circumference to wavelength ratio) x= 1.5 each. Scaled to A=0.8 pm, the size of each sphere is 0.38 p,m and the dimension of the aggregate is 20 pm. Aggregate 2: 37 spheres of size parameter 20 each. Scaled to X=0.8 Jim, the size of each sphere is 5 (im and the dimension of the aggregate is 100 p.m. Aggregate 3: 43 spheres of size parameter jc= 20 each. Scaled to A=0.8 p,m, the size of each sphere is 5 pm and the dimension of the aggregate is 200 p.m.

Figure 4 illustrates the idea how PAM/IDA measurements of polarization of scattered light can be used to classify particles according to their composition.

r= 5 micron

20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160 Scattering angle,deg. Scattering angle,deg.

Figure 4: Transparent and absorbing particles can be distinguished using as few as four r= 5 micron

20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160 Scattering angle,deg. Scattering angle,deg.

Figure 4: Transparent and absorbing particles can be distinguished using as few as four scattering angles. The optical constants are: n = 1.5(—), 1.9 ( ); k= 0.001, 0.005, 0.01,

Shown on Figure 4, results of theoretical (Mie theory) simulation of PAM/IDA measurements demonstrate that transparent and absorbing particles show qualitatively different trends in polarization as a function of scattering angle. For transparent particles polarization is usually low, even negative and has a minimum at medium scattering angles, whereas for absorbing particles polarization is high, positive and gets the maximum at medium scattering angles. The position of the maximum or minimum of polarization depends on the real part of the refractive index. This allows the refractive index m=n+iK of the particle material to be estimated.

3. Laboratory tests of the PAM/IDA

PAM/IDA was tested using transiting water drops. The main purpose of the tests was to show the sensitivity and accuracy of the measurements. Figure 5 shows the results of the measurements in comparison with Mie theory calculations for water spheres.

Figure 5: Particle sizes are in the 36-40 micron diameter range. The solid line is Mie calculations for a 38-micron diameter spherical water drop.

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