Dates of Images:

Pre-Event: 04/20/2024 (pre-flood)

Post-Event: 05/06/2024, 05/07/2024, 05/09/2024, 05/15/2024, 05/21/2024 Time Zone: GMT (local crossing time of ~1:00 pm)

Summary:

This product is the apparent visible wavelength (AVW) of each pixel in a scene, approximating the overall color of the surface. It is calculated by taking the harmonic mean of surface reflectances from 350 nm to 895 nm, and can provide a sense of what has changed in the landscape by comparing several days against each other, as the change in apparent color of a surface often occurs under drastic circumstances. Dates covered include one pre-flood day (04/20/2024) and 5 flood days ending on 05/21/2024 at ~1:00 local time. AVW for each day is delivered, as is a % change from the pre-flood day to each of the 5 flood days afterward, showing the magnitude of color change in the area. Depending on the direction of change, one can infer the type of surface change from AVW. Typically, this metric is calculated from Rrs used for ocean color analyses (see https://doi.org/10.1016/j.rse.2020.111900), but can be made from surface reflectances and used over land as well.

Suggested Use:

Given that AVW is the apparent color of pixel, it can be used to track changes in land and water surfaces. The AVW value indicates average color reflected from a surface, e.g., healthy vegetation will have AVW in the NIR, water in the blues and greens, and turbid water in the reds. During flood days, the area around the Jacui River gets significantly redder (from previous NIR values), which can indicate turbid water supressing the typical vegetated signal in that area. Also, the Lagoa dos Patos gets significantly redder (from the greens), which indicates different conditions in the water (i.e., injection of sediment, which has average colors in the red). Images are typically displayed using the "Spectral" color map, with bounds from 400 - 700 (see attachment). For the percent change images, negative changes signify shorter average wavelengths (can be thought of as blue-shifting) and positive % changes are elongated average wavelengths (i.e., red-shifts). In other words, these shifting wavelengths tell us that some enviornmental change has caused the average color of a pixel to change.

Satellite/Sensor/Resolution:

Satellite: PACE, sensor: OCI, temporal resolution: daily, spatial resolution: gridded to 0.015 degrees from a Level 2 product in instrument swath (varying pixel size, 1.2 km at nadir).

Credits:

Credit: NASA PACE Team, POC: Skye Caplan, Link to data: https://search.earthdata.nasa.gov/search/granules?p=C3620139902-OB_CLOUD&pg[0][v]=f&pg[0][gsk]=-start_date&q=oci%20sfrefl

Dates of Images:

Pre-Event: 04/20/2024 (pre-flood)

Post-Event: 05/06/2024, 05/07/2024, 05/09/2024, 05/15/2024, 05/21/2024 Time Zone: GMT (local crossing time of ~1:00 pm)

Summary:

This product is the apparent visible wavelength (AVW) of each pixel in a scene, approximating the overall color of the surface. It is calculated by taking the harmonic mean of surface reflectances from 350 nm to 895 nm, and can provide a sense of what has changed in the landscape by comparing several days against each other, as the change in apparent color of a surface often occurs under drastic circumstances. Dates covered include one pre-flood day (04/20/2024) and 5 flood days ending on 05/21/2024 at ~1:00 local time. AVW for each day is delivered, as is a % change from the pre-flood day to each of the 5 flood days afterward, showing the magnitude of color change in the area. Depending on the direction of change, one can infer the type of surface change from AVW. Typically, this metric is calculated from Rrs used for ocean color analyses (see https://doi.org/10.1016/j.rse.2020.111900), but can be made from surface reflectances and used over land as well.

Suggested Use:

Given that AVW is the apparent color of pixel, it can be used to track changes in land and water surfaces. The AVW value indicates average color reflected from a surface, e.g., healthy vegetation will have AVW in the NIR, water in the blues and greens, and turbid water in the reds. During flood days, the area around the Jacui River gets significantly redder (from previous NIR values), which can indicate turbid water supressing the typical vegetated signal in that area. Also, the Lagoa dos Patos gets significantly redder (from the greens), which indicates different conditions in the water (i.e., injection of sediment, which has average colors in the red). Images are typically displayed using the "Spectral" color map, with bounds from 400 - 700 (see attachment). For the percent change images, negative changes signify shorter average wavelengths (can be thought of as blue-shifting) and positive % changes are elongated average wavelengths (i.e., red-shifts). In other words, these shifting wavelengths tell us that some enviornmental change has caused the average color of a pixel to change.

Satellite/Sensor/Resolution:

Satellite: PACE, sensor: OCI, temporal resolution: daily, spatial resolution: gridded to 0.015 degrees from a Level 2 product in instrument swath (varying pixel size, 1.2 km at nadir).

Credits:

Credit: NASA PACE Team, POC: Skye Caplan, Link to data: https://search.earthdata.nasa.gov/search/granules?p=C3620139902-OB_CLOUD&pg[0][v]=f&pg[0][gsk]=-start_date&q=oci%20sfrefl