After spending the night in the Mimaka Principality, Jin D set out immediately on the following day, July 11th, to survey the water veins.
First, he started from the point closest to the water source—namely, the Lake Yato side.
Without stopping by the nearby town of Uchidano, he headed straight for the area where an outlet was presumed to be, if one existed at all.
Because the Hurricane lacked tight maneuverability, he used the Eagle Unit 1 instead, with Hope at the controls.
The Hurricane remained on standby in midair. As a security measure, Sky 10 had been summoned as an interim backup pilot.
"All right, it should be somewhere around here... Grand Search... Grand Search... Grand Search."
Jin D cast the underground exploration spell several times in rapid succession.
Incidentally, the one currently piloting Jin D was Jin himself.
Despite the time difference, he had wanted to personally investigate the underground here, no matter what.
"Just as I thought, there's bedrock about 250 meters down. There's an underground water vein above that, capped by a permeable layer roughly 100 meters thick, and finally the topsoil."
Looking at the surrounding terrain, one could infer that around 50 to 100 meters of soil had been piled up in the distant past.
"Time to change locations."
Moving about ten kilometers south and repeating the survey revealed an almost identical underground structure.
He pushed another ten kilometers south, only to find the same results.
"All right, let's make a bigger jump to the south this time."
Jin moved roughly 100 kilometers southward, arriving at an area slightly southeast of the town of Seedra.
"Grand Search... Grand Search... Grand Search... Hmm..."
Aside from the bedrock sitting slightly deeper at 300 meters, the geological structure of this area was virtually unchanged.
"...Hmph."
Analyzing the findings, Jin fell into thought.
"If I keep poking around bit by bit like this, there's no telling how many years it'll take."
Now that his wish to inspect the site firsthand had been satisfied, Jin decided it was time to conduct a proper, comprehensive survey.
Handing control of Jin D over to Laojun, Jin turned his attention to planning the next step.
"...Yeah, it's got to be done that way."
He concluded that a three-dimensional scan was necessary.
"In that case, if I transmit from an ultra-high altitude and use sub-ether waves as a carrier wave..."
Sub-ether waves carried power orders of magnitude greater than standard ether waves, giving them immense penetrating capability. They could pass straight through a planetary crust like that of Planet Ars.
His plan was to use them as a carrier wave to map the subsurface structure.
In principle, it was just like AM radio broadcasting audio by modulating medium waves onto a carrier signal.
"If I scan from the stratosphere, will the distance error be negligible?"
When scanning a broad swath of territory, the difference in distance between the center and the perimeter of the field tended to distort the resulting image.
It was the same optical principle that made noses look oversized and foreheads or chins appear shrunken in ID photos and close-up selfies.
As a side note, conventional photography wisdom once held that an 85mm lens on a 35mm camera was ideal for portraits.
As a further side note, in the modern digital age where images could be retouched at will, that rule of thumb might no longer hold.
"Yes, My Lord. If the scanning area for a single pass is ten kilometers square, an altitude of twenty kilometers would indeed be insufficient."
"Ah, right."
Jin visualized a triangle with a base of ten kilometers and a height of twenty kilometers. He could clearly see that it wouldn't be enough.
"Then what about an altitude of around 100 kilometers?"
"Yes. At that range, calibration would be straightforward, making it ideal."
"Great."
Jin decided to deploy the flagship Adriana for the first time in a while. From her, he wouldn't be limited to 100 kilometers; he could observe directly from outer space.
Besides, for large-scale scanning operations, a larger, heavier, and more stable platform was always preferable.
Without wasting a moment, he rushed to build an Underground Scanner.
The operating principle was simple: fire the Grand Search spell modulated over sub-ether waves.
Because it was controlled by a dedicated compact magi-brain, it could scan dozens of times faster than any human operator.
Jin assembled the device in just twenty minutes and left its installation on the Adriana to the Smiths.
The flagship Adriana was berthed not on Planet Ars, but at the lunar facility Uni.
Jin contacted Jack, the management magi-brain of the Moon.
"Jin-sama, this is Jack."
"Hey. As I explained a moment ago, I want to install an Underground Scanner aboard the Adriana. The Smiths are heading over to your side now, so please give them whatever support they need."
"Understood."
Since the installation and test run would take less than thirty minutes, Jin found himself with a bit of free time.
"Now then, I wonder who's around?"
Since they would be taking the Adriana out into space for the first time in a while, Jin figured someone from the Jin Family might want to tag along, so he put out a call to the members on Hourai Island.
"Mm, I'll go."
"I'm coming too, Onii-chan!"
"Kufu, I could use a little change of pace myself."
"Of course I shall accompany you."
"I'm definitely in."
"If Marcia's going, then count me in as well."
In short order, Elsa, Hanna, Saki, Reinhard, Marcia, and Rodrigo all volunteered.
"All right, let's head out."
The group stepped through the Warp Gate, teleporting directly onto the Adriana.
"Ooh, it has been quite some time since we were last here!" Reinhard exclaimed.
Because they had been using Warp Gates to travel to and from Planet Hehl, it had been a long while since any of them had boarded a spaceship.
Before long, word came in that the Underground Scanner had been installed and had passed its operational tests without a hitch.
"All right, let's get moving....Taisei, take the helm."
"Yes, My Lord."
Overseeing and operating the colossal spherical spaceship Adriana was the magi-brain Taisei.
Cosmos units 1 through 500 of the Space Force golems staffed the ship as its crew.
The Adriana lifted off from the base on the Moon, Uni.
Accelerating toward Planet Ars at 10G, Jin and the others settled in to enjoy the brief space flight.
"The stars really are magnificent when seen from space."
"Mm."
Jin and Elsa stood shoulder to shoulder in the private Observation Room, gazing out at the sea of stars.
Multiple barriers shielded the room, granting complete peace of mind by filtering out all hazardous cosmic rays and radiation while letting only visible light pass through.
"Ah, there you are, Jin!"
"Father."
"This spot truly offers the finest view, after all."
About thirty minutes later, Reinhard, Reiko, and the others walked in.
"Did you two enjoy your moment alone?"
"Er, well..."
It seemed the rest of the group had tactfully held back to give them some privacy.
"Father, Marcia-san and Rodrigo-san mentioned that they have something they would like to discuss with you."
"Oh? What is it?"
As they took their seats around the table in the Observation Room, Reiko served drinks for everyone.
Basking in the relaxed, comfortable atmosphere, Jin and the others settled down to talk.