NASA's Land, Atmosphere Near real-time Capability for Earth observation (LANCE) provides two global daily ~250 m resolution near-real time (NRT) flood products:

• MODIS product (MCDWD) generated from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument imagery on the Terra and Aqua platforms.
• VIIRS product (VCDWD) generated from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument imagery on the NOAA-20 (JPSS-1) and NOAA-21 (JPSS-2) platforms.

The VIIRS product was released in April 2025. Apart from the difference in input data source (MODIS or VIIRS), the products are otherwise the same in algorithm and product formats. With the Terra and Aqua satellites expected to be retired in 2026-27, the VIIRS product was developed to replace the MODIS product.

The FLOOD viewer facilitates the use and evaluation of these flood products by allowing the user to browse globally and over time and compare to other flood products. Initially the NOAA-GMU VIIRS flood product has been included, along with the NASA JPL OPERA surface water product (based on Landsat + Sentinel-2 imagery).

In the viewer, the default “Basic” mode provides a simplified interface with fewer flood products for new users to explore (it only includes the 2-day composite product, as this is generally recommended for an initial look). The Advanced tab adds the 1-day and 3-day products, along with other flood and water products.

If no clouds are present, the 1-day product is likely the most useful and up-to-date. However, in the presence of clouds, the 1-day product can be contaminated with cloud-shadow false-positives, so the user must compare the source imagery (in the MODIS/VIIRS imagery group) to the flood product. These can also occasionally affect the 2-day product, so it is always recommended to review the visible imagery in conjunction with the flood products.