Geodesy is the science of determining the Earth's shape, it's rotation and gravity field. Including it's variation in time.

So, here is one example illustrating a segment of the shape of the Earth. I personally monitor this particular part of the Earth - and it's variations in time. That implies multiple hiking expeditions every year - all seasons. :-)

Even though the shape remains the same, it looks different depending on the light and state of the biosphere (with or without leaves on the trees...). Of course the shape is altered by the snow, and that vary every year, but apart from that the shape seems intact. Using my body as a gravimeter, I can conclude that the gravity seem pretty stable.

Geodesy, people, this is geodesy! :-)

PS. Normally we use GPS, VLBI, GOCE&GRACE, superconducting gravimeters, a number of other otherwordly super cool satellites to measure the shape, rotation and gravity field. I just go hiking to enjoy  the landscape. :-)