## Thursday, June 22, 2023

### A Ph.D. position on Po River, DARTHs, Earth Observations

It looks like it is very dedicate to informatics (see also here) but let me say that the candidate should write their  project with a broader view, although it must remain within the scope of what we are doing in the context of the Po River basin project and  related to the exploitation of satellite data to support hydrological modeling. The project that funds it, besides PNRR,  is 4DHYdro, which collects some of the best hydrological modellers in Europe (and from the projects' goal you can find inspiration).

The general focus of the study are droughts and can contains more computer science-related parts, more conceptual parts, or more applied parts. The themes related to the processes are: snow, plant transpiration, and crop needs. The enabling technology is precisely the systematic use of Earth observation, and the concept paper for the whole system is the one about DARTHs. Further information on DARTHs can be found here

If, at this point, you are a little convinced to apply also consider the philosophy of our group that you can find in a sequence of posts, here and and links therein.

Our group is a  crew of international fellows: 2 Indians, 1 Pakistani, 1French, 1 Iranian, 1 Algerian and 8 Italians, including two professors, one researcher (at Eurac), two postdocs, and nine Ph.D. students already.

## Saturday, June 10, 2023

### Transit time, Residence time, Response time, Life expectancy

Just to help someone, a few definitions:

• Travel Time (a.k.a. Transit Time), T: It is the time a parcel of water stays inside a control volume. If $t_{in}$ is the time it entered the control volume and $$t_{ex}$$ the travel time it exits, then $$T= t_{ex}-t_{in}$$ For an observer placed at the outlet(s) of the control volume, since their actual (clock) time coincides with $$t_{ex}$$, i.e $$t_{ex}=t$$ it is $$T= t-t_{in}$$. The actual variable in this definition is $$t_{in}$$

• Residence time is $$T_R = t-t_{in}$$
• Life expectancy is $$T_L = T_{ex} - t$$ so, it is also: $$T = T_R+T_L$$
• Response time is $$R = t_{ex}-t_{in}$$ but only restricted to all the parcels injected at the same $$t_{in}$$ estimated at $$t=t_{in}$$ and is their life expectancy at  $$t=t_{in}$$. The actual variable here is $$t_{ex}$$.
All of these definitions are given in statistical sense, meaning that they are stochastic variables described trough their distributions. Looking at the above definitions  and if we do not read them very carefully, it looks like that transit time and response time are the same thing and we though for decades it was. Instead they are not since transit time distribution is conditional to the clock time, while response time distribution is conditional to the injection time.  The first is a distribution in $$t_{in}$$, the second in $$t_{ex}$$.