Google Earth Engine (GEE) applications in hydrology

class: center, middle, inverse, title-slide

# Google Earth Engine (GEE) applications in hydrology
### Josh Erickson
### USDA-Forest Service

---

## About Me

- Hydrologist (day job)
- Remote Sensing Analyst (detail)
- Geoscience and Math background
- Focus is leveraging computing platforms (R, Python, GEE) for resource management work.

.me-box[]
---

## Goals
--

- Leave having an idea of what GEE is and what it can do

<img src="gee_talk_files/images/gee.png" height="50px" right: 25%/>
 
 
- Most importantly, some applications in hydrology

.water-box[]

- What, how, apply.

---

## What is GEE?
--

- free open source software .blue[(FOSS)]

- Inherently parrallel; uses a .blue[petabyte] scale server ~ 1,000,000 GB

- allows .blue[clients (users)] to ask for products (Image/ImageCollections)

- And then will process those requests .blue[server-side]

---

## Advantages
--

- Extensive collections (e.g. imagery, geophysical, weather/climate models, etc.)

- Reducing big ImageCollections

- Fast, really really fast!

- Lots of documentation, apps, tutorials, research, etc.

.ferrari-box[

]

## Disadvantages (IMO)

- Can be 'coding' barrier entry

- Can be abstract-ish, i.e. remote sensing

- Research buzz...

.problems-box[]

---

## Reduce Image (The how?)

A big advantage of earth engine is to reduce large image collections fast.

.bg-washed-green.b--dark-green.ba.bw2.br3.shadow-5.ph4.mt5[
For example, let's say we want the median PRISM monthly precipitation from 2010-present]
 
 
<center>
<img src="gee_talk_files/images/precip_intro.png" height="200px" align="bottom" />
</center>

---

## Reduce Image (The how?)

.pull-left[
<center>

</center>
]

.pull-right[

</center>
]

---

## Applying the Concept
Reduce Regions is the key; points and polys. 
Very similar to `extract` in ArcGIS
.pull-left[

]

.pull-right[
.rrhucs-box[]
]

---

## Applying the Concept
Reduce Regions is the key; points and polys. 
Very similar to `extract` in ArcGIS
.pull-left[

]

.pull-right[
.rrPts-box[]
]

---

## You can provide any geometry

- For example, proposed land use activities.

---

## Layer units by images

.units-box[]

---

## Now we have zonal stats for each unit!

.unitsrr-box[]

---

## What about time series?
Not going to get too crazy but you can.

`\(\hat{Y}_t = a_0 + \sum_{n=1}^\infty (a_n\cos nx +b_n\sin nx)\)`

.deep-box[]

Just keep it simple

---

# Banding

This is a way to keep a certain temporal feature, e.g. year, month, week, etc.

.pull-left[

]

.pull-right[
<img src="gee_talk_files/images/to_bands.png" height="300px" />
]

---
# Example with previous points

.pull-left[

]

.pull-right[

]

---
# Example with previous points

---

# Animation with time series

---

# Animation with time series

---
# Animation with time series

---

# Animation with time series

---

# Into the future?
<center>
<img src="https://media.giphy.com/media/ZZkCo8zKWtt2ZgozfX/giphy.gif" height="500px" />
</center>

---
# Into the future?

There are available climate models in GEE. NASA Earth Exchange.

---
# Into the future?

What about the units we looked at?

.pull-left[
<img src="gee_talk_files/images/units.png" height="300px" />
]

.pull-right[
<img src="gee_talk_files/images/future_temp_box.png" height="400px" />
]

---
# Wrapping Up

- GEE is a way to .blue[reduce] big image collections

.pull-right[

</center>
]

- You can do it from local to regional .blue[scale]

.pull-right[

</center>
]

- Climate projections into the .blue[future]

.pull-right[

</center>
]

---

# Wrapping Up

- slides available at https://hydroblog.org/slides/gee_talk/gee_talk.html

- some apps from Justin Braaten; https://emaprlab.users.earthengine.app/view/lt-gee-time-series-animator, https://t.co/xqUN7W8KBa?amp=1, https://t.co/3fTl0wI8Gh?amp=1
<center>
.end-box[]
</center>