Several important bio-optical models have been developed to describe the interactions between light and the biological and optical properties of natural waters. These models are foundational in aquatic remote sensing, oceanography, and water quality studies. Here are some of the most significant ones:
1. Gordon and Morel Models
- Creators: Howard R. Gordon and André Morel
- Description: These are foundational models that relate inherent optical properties (IOPs) like absorption and scattering to apparent optical properties (AOPs) like reflectance and radiance.
- Applications:
- Used in interpreting satellite and in situ data to estimate parameters like chlorophyll-a concentration.
- Gordon’s model laid the groundwork for many remote sensing algorithms.
2. The Quasi-Analytical Algorithm (QAA)
- Creator: ZhongPing Lee and collaborators
- Description: QAA is a semi-analytical model used to retrieve IOPs (such as absorption and backscattering coefficients) from remote sensing reflectance data.
- Applications:
- Widely used in ocean color remote sensing.
- Can work across diverse water types, from clear oceanic to turbid coastal waters.
3. Morel and Prieur Model (1977)
- Creators: André Morel and Louis Prieur
- Description: This classic model distinguishes between the optical properties of case 1 waters (phytoplankton-dominated) and case 2 waters (dominated by CDOM or suspended particles).
- Applications:
- Formed the basis for many modern ocean color algorithms.
- Focuses on phytoplankton as the dominant light-modifying component in open oceans.
4. Hydrolight Model
- Creator: Curt Mobley
- Description: Hydrolight is a radiative transfer model that simulates light propagation in water, accounting for both IOPs and environmental conditions (e.g., sky conditions, water depth).
- Applications:
- Used for simulating light fields and refining remote sensing algorithms.
- Suitable for detailed, site-specific studies.
5. Case 2 Regional/Coastal Models
- Example: The Case 2 Waters Bio-Optical Model developed as part of the European Space Agency’s MERIS project.
- Description: These models are tailored for complex coastal and inland waters (case 2 waters) where multiple substances (phytoplankton, CDOM, and sediments) influence optical properties.
- Applications:
- Used for water quality monitoring in regions where standard oceanic models fail.
6. Ocean Color Component Models
- Examples: OC2, OC4, and OCx algorithms
- Description: Empirical models developed by NASA for estimating chlorophyll-a concentration from satellite data (e.g., MODIS, SeaWiFS).
- Applications:
- Designed for global ocean monitoring.
- Derived from bio-optical relationships in case 1 waters.
7. Two-Component Models
- Creators: Multiple contributors, such as IOCCG (International Ocean Colour Coordinating Group)
- Description: These models decompose water reflectance into contributions from phytoplankton, CDOM, and suspended matter.
- Applications:
- Useful for retrieving concentrations of specific water constituents.
8. Generalized Inherent Optical Properties (GIOP) Model
- Developed By: NASA and collaborators
- Description: A flexible framework for deriving IOPs from remote sensing data by combining different parameterizations of absorption and scattering.
- Applications:
- Allows customization to specific water types.
- Supports global ocean color products.
9. Nechad Reflectance-Based Algorithms
- Creator: Benoît Nechad et al.
- Description: Empirical algorithms that link remote sensing reflectance to suspended particulate matter (SPM) and turbidity.
- Applications:
- Widely used for monitoring sediment dynamics in estuarine and coastal waters.
10. Semianalytical Bio-Optical Algorithm (SABOA)
- Creator: Various researchers
- Description: A semi-analytical model designed for estimating chlorophyll, CDOM, and SPM concentrations in optically complex waters.
- Applications:
- Particularly effective in case 2 waters, including inland and coastal environments.
Comparison of Bio-Optical Models
| Model | Type | Water Types | Focus |
| Gordon & Morel | Empirical | Open ocean | AOP-IOP relationships |
| Hydrolight | Physical | All types | Radiative transfer |
| QAA | Semi-analytical | All types | IOP retrieval |
| Morel & Prieur | Theoretical | Open ocean | Case 1 waters |
| Nechad Algorithms | Empirical | Coastal | SPM and turbidity |
| Ocean Color Models | Empirical | Open ocean | Chlorophyll estimation |