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Incorporate Josh's feedback

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sources/01c-coverage-analysis.ipynb
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@ -98,7 +98,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"All available products are plotted to verify if there are enough products to cover our area of interest without holes.\n",
"All available products are plotted to verify that there are enough products to cover the area of interest without holes.\n",
"As the revisit frequency given by the Sentinel-2 mission is much lower than four weeks this should not be a problem."
]
},
@ -264,7 +264,7 @@
"Adjacent rectangles are not perfectly parallel.\n",
"This is because of choices that have to be made when projecting from the earths spherical surface to a rectangular plane.\n",
"The UTM grid is constructed so that coordinates within each tiling represent metrical distances on the earths surface.\n",
"This has the nice property that in order to areas and surfaces within a UTM tiling can be calculated simply by counting.\n",
"This has the nice property that lengths and areas within a UTM tiling can be calculated simply by counting pixels or using Euclidian distance arithmetic.[^in_contrast_to_lat_lon]\n",
"\n",
"(content:orbits)=\n",
"## Product Shape and Orbit Number\n",
@ -272,8 +272,9 @@
"As mentioned above, each square is a single product that can be downloaded from the Copernicus Open Access Hub.\n",
"The visualizations above and the true color rendering in [](01b-visualization.ipynb) shows that these products are not often not perfect squares, but that they have missing slices.\n",
"\n",
"This is because of the satellite orbit at the time of capturing the data.\n",
"To visualize this we plot the available products per orbit:"
"This is because of path along which the satellite orbits the Earth, which can be shown by plotting the available products per orbit number:\n",
"\n",
"[^in_contrast_to_lat_lon]: This is in contrast to Coordinate Reference Systems which use Latitude and Longitude, such as the widely used WGS84, which does not express coordinates on a plane, and has to rely on more complex eliptical distance calculations."
]
},
{
@ -398,9 +399,9 @@
"source": [
"## Ensuring Complete Coverage\n",
"\n",
"If we do not want to wait an entire repeat cycle, what is the minimum time span in those four weeks to ensure a coverage of all of Brandenburg?\n",
"When not waiting for an entire repeat cycle to complete, what is the minimum time span in those four weeks to ensure complete data for Brandenburg?\n",
"\n",
"To find out we iterate through the returned products, for each iteration $i$ unifying the associated product's geometry $P_i$ with all products we already iterated through:\n",
"To answer this question, the returned products are iterated through. For each iteration $i = I$ the associated product's geometry $P_{i=I}$ is unified with all products $P_{i<I}$:\n",
"\n",
"\\begin{align*}\n",
" P &= \\{P_1, P_2, \\cdots, P_n\\} \\\\\n",
@ -523,7 +524,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"We re-use the `plot_downloaded_products` to get a visual impression of the area of the union of tiles just created:"
"The function `plot_downloaded_products` is reused to get a visual impression of the area of the union of tiles just created:"
]
},
{
@ -563,7 +564,7 @@
"metadata": {},
"source": [
"The algorithm worked, the entire area is comfortably covered.\n",
"We can calculate the time span over which the subselection was captured:"
"The time span over which the subselection was captured is 3 days:"
]
},
{
@ -591,7 +592,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"Compare this to the repeat cycle observed in [](content:orbits):"
"This is a lot lower than the repeat cycle observed in [](content:orbits):"
]
},
{
@ -620,10 +621,10 @@
"source": [
"### Cloud Coverage\n",
"\n",
"For the union above we did not consider cloud coverage at all.\n",
"The union calculation above did not consider cloud coverage at all.\n",
"This means that a lot of pixels in the large area of interest might not have interesting data for us:\n",
"\n",
"A plot of the cloud coverage can give us an estimate of how useful the combined image would be without needing to plot it visually as described in [](01b-visualization.ipynb):"
"A plot of the cloud coverage can give an estimate of how useful the combined image would be without needing to plot it visually as described in [](01b-visualization.ipynb):"
]
},
{
@ -655,7 +656,7 @@
"The histogram shows that some of the products consist mostly of cloudy pixels - in fact, the relationship between cloudy and non-cloudy pixels is almost symmetrical.\n",
"A cloud coverage of 100% is not of much use for us because it amounts to an image that does not contain any of the surface features we are interested in.\n",
"\n",
"To include only less cloudy products, a compromise on up-to-dateness hast to be made.\n",
"To include only less cloudy products, a compromise on up-to-dateness has to be made.\n",
"Setting a maximum cloud coverage of 50% increases the time delta to 15 days:"
]
},
@ -778,7 +779,7 @@
"cell_type": "markdown",
"metadata": {},
"source": [
"Downloads are expensive because each product to be downloaded has a size of approximately 1GB. We try to reduce the amount of products we need to download by dropping identical geometries, keeping the one with the smallest cloud cover:"
"Downloads are expensive because each product to be downloaded has a size of approximately 1GB. The amount of products to download is reduced by dropping identical geometries, keeping the one with the smallest cloud cover:"
]
},
{