FDTD simulations - Why Smooth Turn-on of Source is Needed?

In Finite-Difference Time-Domain (FDTD) simulations, source injection needs to be smoothly done in order to suppress the undesired high frequency components excited during turn on. To visualize this problem, we provide two cases with and without turn-on source injection. On the right simulation, total field/scattered field injection is done using the cosine excitation without any smooth turn-on which effectively mimics the step function operation. This results in the injection of high frequency components creating the ripples and fluctuations in the signal propagating in the domain. On the contrary, the left simulation has a smooth turn of by using a half Hanning window ramp-up which effectively acts as low pass filter for the injected source. As a result, the signal propagating in the domain is free of high frequency components, hence no ripples and fluctuations.

Nehalem Bay from the Neahkahnie Mountain [1,680' (512 m)]

Finally, we had an opportunity to have a family hike this summer. My son, Omer and my daughter, Meryem were with us as well. Omer was walking by himself and Meryem was comfortably carried in my back. After a pleasant  hour of walking starting from the south trailhead, we reached to the top of Neahkahnie Mountain. The view of the Nehalem Bay and the Pacific Ocean was stunning. Omer was happy to be at the top and couldn't help but took his selfie.

Mt. Hood Walk Up to 2915 m (9563 ft)

Seems so simple in the GPS track log. But in reality, it poses both physical and mental challenges to walk up to Mt. Hood. And definitely, it requires well studied planning from what to have in your backpack to what to eat before the start etc. After the attempt, I now realize that I wasn't well prepared for the challenge. My crampons were not fitting very well and at every step my mind was preoccupied whether they would get out of my shoes or not. The glasses I brought and started using after 2500 m where not fog proof. So, with the influence of sweat and breath warmth, the glasses became foggy making me half blind. After 2500 m, the wind was strong and the weather got really cold. I didn't have anything to cover my face and it got really cold. Eventually, I started to have headache which grew only bigger. I started to feel so sleepy and they told me that I was going through altitude sickness. Hence I needed to get down as quick as possible. I had to abort the climb. I was ~100 m away from the Hog's Back. Hopefully, next time with better preparation I can do better than this one.

Here are some photos from that day:
Mt. Hood right before the sunset as seen from Timberline Lodge. Getting ready for the midnight walk-up.

The walk-up starts around 1 am and the trail is already full of fellow hikers lighting up the trail.

Sun is rising behind the Mt. Hood. Since we are in the south-west side, we are left in the shade. Mt. Jefferson is seen at the background.

At 2915 m (9563 ft), altitude sickness kicks in. I have a very bad headache and drowsiness. Cannot continue further, need to turn back. This is the last point I was able to reach close to the Hog's Back.

Canyon right on the south of Hog's back.

Mt. Hood

Munra Point Hike (573 m -1879 ft)

Some photos

McNeil Point Hike at the Mt. Hood National Forest (2118 m ~ 6900 ft)

Here is the video of the last 100 meters of hike past the McNeil point towards Mt Hood from the Cathedral Ridge.



Photos:
Mt Hood from the North side. Glisan Glacier is on the left and Cathedral Ridge to Mt Hood is just in front of us. 

 Looking northwards. On the horizon, Mt. Adams can be seen.

 The valley on the south side of McNeil Point.

GPS log of our hike: