Sonar Explained: CHIRP vs. DownScan vs. Side Imaging

Most anglers don’t have a fish-finding problem.

They have a sonar-reading problem.

And until that’s fixed
no upgrade will make a difference.

I’ve seen high-end setups struggle…
and simple setups outperform them.

The difference isn’t the technology.

It’s understanding.

Because CHIRP, DownScan, and Side Imaging are not interchangeable tools.
Each one solves a specific problem.

Use them correctly, and everything becomes clear.
Use them wrong, and your screen turns into noise.

This guide will show you the difference
in a way that actually makes sense on the water.

We’ll go through:

• How sonar actually works
• The real difference between CHIRP, DownScan, and Side Imaging
• When to use each one in real fishing situations
• And the best setups you can use without wasting money

Sonar Fundamentals

Before we jump into CHIRP, DownScan, and Side Imaging, you need to understand one thing clearly:

If you do not understand how sonar works,
You’ll misread everything on your screen.

Let me simplify it for you.

What Sonar Actually Is

Sonar stands for Sound Navigation and Ranging.

At its core, sonar operates on a simple principle:

Send → Bounce → Return → Display

That’s it.

Your unit isn’t “seeing” underwater.
It’s interpreting sound.

How Sonar Works

Here’s what’s happening every second under your boat:

• The transducer sends sound waves into the water
• Those waves hit:
  • Fish
  • Bottom
  • Structure
• The echo comes back
• Your unit converts that into an image on your screen

What you’re looking at is not a picture.
It’s a processed signal.

The 4 Variables That Control Everything

This is where most anglers get it wrong.

These four things control what you see:

1. Frequency

• Low frequency → deeper penetration
• High frequency → more detail

2. Power

• Stronger signal → deeper reach
• Also gives cleaner returns in tough conditions

3. Cone Angle

• Wide cone → covers more water, less detail
• Narrow cone → more detail, less coverage

4. Ping Rate

• Faster ping → smoother, more real-time image
• Slower ping → laggy, less accurate tracking

The Frequency Rule (This Changes Everything)

If you understand this, everything else becomes easier:

• 80–83 kHz → deep water, low detail
• 200 kHz → balanced
• 455 / 800 / 1200 kHz → great detail, shallow water

Higher frequency shows detail. Lower frequency finds depth.

Learn more about Lowrance’s official guide to sonar frequency and transducer basics

CHIRP Sonar (Best for Finding Fish)

Now that you understand the basics, let’s talk about the most important one first

CHIRP sonar.

If you’re using chirp sonar-GPS combos,

This feature plays a crucial role in locating fish.

What Is CHIRP Sonar

CHIRP stands for one key idea:

Instead of sending a single frequency…
It sends a continuous sweep of frequencies.

Simple example:

• Traditional sonar → 200 kHz only
• CHIRP sonar → 150–250 kHz range

That’s a big difference.

How CHIRP Works

Here’s what’s happening behind the scenes:

• It sends a range of frequencies into the water
• Receives multiple return signals
• Combines them into a cleaner, more accurate image

More data = better clarity

Types of CHIRP

Different ranges are used for different depths:

• Low CHIRP (40–60 kHz) → deep water
• Medium CHIRP (80–160 kHz) → balanced
• High CHIRP (150–250 kHz) → more detail

Why CHIRP Works So Well

This is why most modern anglers rely on it:

• Better target separation (you can distinguish fish clearly)
• Cleaner, more defined fish arches
• Less noise and interference
• Performs extremely well in deep water

Where CHIRP Falls Short

It’s not perfect.

• Doesn’t show the exact shape of the structure
• Less “photo-like” detail compared to imaging sonar

It tells you something is there… but not exactly what it is

Real-World Use

CHIRP shines when:

• You’re offshore fishing
• Looking for suspended fish
• Scanning deep water

CHIRP answers: “Are there fish here?”

DOWNSCAN IMAGING (Best for Understanding Structure)

If CHIRP tells you something is there
DownScan tells you exactly what it is.

This is where things start to get visually clear.

What Is DownScan

DownScan is a high-frequency imaging sonar that looks straight down beneath your boat.

It’s built for one thing: Clarity

How It Works

• Uses very high frequencies (455–1200 kHz)
• Sends a narrow beam
• Produces a near photo-like image

Because of that narrow beam, you get way more detail compared to traditional sonar.

What Makes It Different

This is where most people get confused.

DownScan doesn’t look like CHIRP at all:

• No arches
• Fish show up as small dots or specks
• The structure appears extremely sharp and defined

Why It’s So Powerful

• Extremely high detail
• Perfect for identifying:
  • Rocks
  • Brush piles
  • Drop-offs
  • Wrecks

This is how you stop guessing.

Where It Falls Short

• Limited coverage (only directly below)
• Not ideal for deep water scanning

Real-World Use

DownScan is best when:

• You’re inshore fishing
• Fishing around structure
• Doing jigging or drop shot

DownScan answers: “What exactly is below me?”

Side Imaging (Best for Finding New Spots Fast)

If DownScan shows you what’s below…
Side imaging shows you what’s around you.

This is how anglers stop fishing blindly and start fishing strategically.

What Is Side Imaging

Side imaging is sonar that scans left and right of your boat instead of just looking down.

• You’re no longer limited to what’s under you
• You can see what’s happening far out to the sides

How It Works

• Sends sonar beams sideways
• Covers roughly 200–400 feet per side
• Uses high-frequency signals for detail

This gives you a wide underwater view, almost like a map.

What You Actually See

This is where it gets powerful but also tricky:

• Shadows (this is critical to learn)
• Structure position relative to your boat
• Fish schools off to the side

The shadow tells you height and shape.
The object tells you what’s there.

Strengths

• Covers massive areas quickly
• Helps you find:
  • Drop-offs
  • Channels
  • Wrecks
  • Fish schools

Instead of searching blindly, you scan efficiently.

Weakness

• Takes time to learn and interpret
• Less detailed than DownScan directly below
• Affected by boat speed and movement

It’s powerful but not beginner-friendly at first.

Real-World Use

Side imaging shines when:

• You’re scouting new waters.
• Searching offshore areas
• Trying to locate fish before positioning your boat

Side imaging answers the question, “Where should I fish?”

CHIRP vs DownScan vs Side Imaging

• CHIRP = Detection
• DownScan = Identification
• Side Imaging = Exploration

When to Use Each (Real Fishing Scenarios)

This is the part most anglers miss.

It’s not about choosing one sonar

It’s about using them in sequence based on the situation.

Here’s the simplest way to think about it:

Offshore (Deep Water Fishing)

• Start with CHIRP → Find suspended fish in deep water
• Use Side Imaging → Scan around for bait schools or structure
• Switch to DownScan → Confirm what’s directly below (wreck, reef, bottom detail)

Flow: Find → Scan → Confirm

Inshore (Structure Fishing)

• Start with side imaging → Locate structure (grass, docks, rocks)
• Use DownScan → Identify exactly what that structure is
• Use CHIRP → Check if fish are holding there

Flow: Locate → Understand → Confirm

Fishing New / Unknown Water

• Start with side imaging. → Cover large areas quickly
• Use DownScan → Break down promising spots
• Use CHIRP → Confirm fish presence before fishing

Flow: Search → Analyze → Validate

Do you want to know more about inshore & offshore fishing? Read this guide.

Common Mistakes Anglers Make with Sonar

Most sonar issues aren’t because of bad equipment.

They happen because of how the sonar is being used.

Here are the biggest mistakes. Keep these in mind,

and you’ll instantly read your screen better:

• Using the wrong frequency for the depth
  • High frequency in deep water = weak signal
  • Low frequency in shallow water = no detail
  • Result: You see unclear or misleading data
• Ignoring transducer power
  • Low power struggles in deep or dirty water
  • Your screen may look clean, but you’re missing fish
• Confusing fish with structure
  • Bait, debris, and bottom can look similar.
  • This is why relying on only one sonar type creates mistakes
• Using only one sonar mode
  • CHIRP alone = you don’t understand structure
  • Down scan alone, and you miss fish movement.
  • The real advantage comes from combining them
• Moving too fast with Side Imaging
  • High speed distorts the image.
  • You lose detail and misread structure

Final Takeaway

Let’s simplify everything.

• If your goal is to find fish → use CHIRP
• If your goal is to understand structure → use DownScan
• If your goal is to cover water fast, → use side imaging.

That’s it.

But here’s where most anglers level up:

• The best setup is not choosing one
  It’s using all three together

That’s how you go from guessing… to fishing with confidence.

Still not sure which sonar setup fits your fishing style?

Choosing the wrong unit can cost you fish and money.

Get expert help and pick the right CHIRP sonar GPS combo for your water.

Frequently Asked Questions